Hydrogen (H) is a very light chemical element, with a content of 0.9% by mass in the Earth's crust and 11.19% in water.
Characterization of hydrogen
In terms of lightness, it is the first among gases. Under normal conditions, it is tasteless, colorless, and absolutely odorless. When it enters the thermosphere, it flies into space due to its low weight.
In the entire universe, it is the most numerous chemical element (75% of the total mass of substances). So much so that many stars in outer space are composed entirely of it. For example, the Sun. Its main component is hydrogen. And heat and light are the result of the release of energy during the fusion of the nuclei of the material. Also in space there are whole clouds of its molecules of various sizes, densities and temperatures.
Physical Properties
High temperature and pressure significantly change its qualities, but under normal conditions it:
It has a high thermal conductivity when compared with other gases,
Non-toxic and poorly soluble in water
With a density of 0.0899 g / l at 0 ° C and 1 atm.,
Turns into a liquid at -252.8°C
Becomes solid at -259.1°C.,
The specific heat of combustion is 120.9.106 J/kg.
It requires high pressure and very low temperatures to become liquid or solid. When liquefied, it is fluid and light.
Chemical properties
Under pressure and cooling (-252.87 gr. C), hydrogen acquires a liquid state, which is lighter in weight than any analogue. In it, it takes up less space than in gaseous form.
He is a typical non-metal. In laboratories, it is obtained by reacting metals (such as zinc or iron) with dilute acids. Under normal conditions, it is inactive and reacts only with active non-metals. Hydrogen can separate oxygen from oxides, and reduce metals from compounds. It and its mixtures form hydrogen bonds with certain elements.
The gas is highly soluble in ethanol and in many metals, especially palladium. Silver does not dissolve it. Hydrogen can be oxidized during combustion in oxygen or air, and when interacting with halogens.
When combined with oxygen, water is formed. If the temperature is normal, then the reaction is slow, if above 550 ° C - with an explosion (turns into explosive gas).
Finding hydrogen in nature
Although there is a lot of hydrogen on our planet, it is not easy to find it in its pure form. Little can be found during volcanic eruptions, during oil extraction and in the place of decomposition of organic matter.
More than half of the total amount is in the composition with water. It is also included in the structure of oil, various clays, combustible gases, animals and plants (the presence in every living cell is 50% by the number of atoms).
Hydrogen cycle in nature
Every year, a huge amount (billions of tons) of plant remains decompose in water bodies and soil, and this decomposition splashes a huge mass of hydrogen into the atmosphere. It is also released during any fermentation caused by bacteria, combustion and, along with oxygen, participates in the water cycle.
Applications for hydrogen
The element is actively used by humanity in its activities, so we have learned how to get it on an industrial scale for:
Meteorology, chemical production;
production of margarine;
As fuel for rockets (liquid hydrogen);
Power industry for cooling electric generators;
Welding and cutting of metals.
The mass of hydrogen is used in the production of synthetic gasoline (to improve the quality of low-grade fuel), ammonia, hydrogen chloride, alcohols, and other materials. Nuclear power actively uses its isotopes.
The preparation "hydrogen peroxide" is widely used in metallurgy, the electronics industry, pulp and paper production, in the bleaching of linen and cotton fabrics, in the manufacture of hair dyes and cosmetics, polymers, and in medicine for the treatment of wounds.
The "explosive" nature of this gas can become a deadly weapon - a hydrogen bomb. Its explosion is accompanied by the release of a huge amount of radioactive substances and is detrimental to all living things.
The contact of liquid hydrogen and the skin threatens severe and painful frostbite.
distribution in nature. V. is widely distributed in nature, its content in the earth's crust (the lithosphere and hydrosphere) is 1% by mass and 16% by the number of atoms. V. is part of the most common substance on Earth - water (11.19% of V. by mass), in the composition of the compounds that make up coal, oil, natural gases, clay, as well as animal and plant organisms (i.e., in the composition proteins, nucleic acids, fats, carbohydrates, etc.). In the free state, V. is extremely rare; it is found in small quantities in volcanic and other natural gases. Negligible amounts of free V. (0.0001% by number of atoms) are present in the atmosphere. In the near-Earth space, V. in the form of a stream of protons forms the internal (“proton”) radiation belt of the Earth. In space, V. is the most common element. In the form of plasma, it makes up about half the mass of the Sun and most stars, the main part of the gases of the interstellar medium and gaseous nebulae. V. is present in the atmosphere of a number of planets and in comets in the form of free H2, methane CH4, ammonia NH3, water H2O, radicals such as CH, NH, OH, SiH, PH, etc. In the form of a stream of protons, V. is part of the corpuscular radiation of the Sun and cosmic rays.
Isotopes, atom and molecule. Ordinary V. consists of a mixture of two stable isotopes: light V., or protium (1H), and heavy V., or deuterium (2H, or D). In natural compounds of V., there are on average 6,800 1H atoms per 1 2H atom. A radioactive isotope has been artificially obtained - superheavy B., or tritium (3H, or T), with soft β-radiation and a half-life T1 / 2 = 12.262 years. In nature, tritium is formed, for example, from atmospheric nitrogen under the action of cosmic ray neutrons; it is negligible in the atmosphere (4-10-15% of the total number of atoms of air). An extremely unstable 4H isotope has been obtained. The mass numbers of the isotopes 1H, 2H, 3H and 4H, respectively 1,2, 3 and 4, indicate that the nucleus of the protium atom contains only 1 proton, deuterium - 1 proton and 1 neutron, tritium - 1 proton and 2 neutrons, 4H - 1 proton and 3 neutrons. The large difference in the masses of isotopes of hydrogen causes a more noticeable difference in their physical and chemical properties than in the case of isotopes of other elements.
The atom V. has the simplest structure among the atoms of all other elements: it consists of a nucleus and one electron. The binding energy of an electron with a nucleus (ionization potential) is 13.595 eV. The neutral atom V. can also attach a second electron, forming a negative ion H-; in this case, the binding energy of the second electron with the neutral atom (electron affinity) is 0.78 eV. Quantum mechanics makes it possible to calculate all possible energy levels of the atom, and, consequently, to give a complete interpretation of its atomic spectrum. The V atom is used as a model atom in quantum mechanical calculations of the energy levels of other, more complex atoms. The B. H2 molecule consists of two atoms connected by a covalent chemical bond. The energy of dissociation (i.e., decay into atoms) is 4.776 eV (1 eV = 1.60210-10-19 J). The interatomic distance at the equilibrium position of the nuclei is 0.7414-Å. At high temperatures, molecular V. dissociates into atoms (the degree of dissociation at 2000°C is 0.0013; at 5000°C it is 0.95). Atomic V. is also formed in various chemical reactions (for example, by the action of Zn on hydrochloric acid). However, the existence of V. in the atomic state lasts only a short time, the atoms recombine into H2 molecules.
Physical and chemical properties. V. - the lightest of all known substances (14.4 times lighter than air), density 0.0899 g / l at 0 ° C and 1 atm. V. boils (liquefies) and melts (solidifies) at -252.6°C and -259.1°C, respectively (only helium has lower melting and boiling points). The critical temperature of V. is very low (-240 ° C), so its liquefaction is associated with great difficulties; critical pressure 12.8 kgf/cm2 (12.8 atm), critical density 0.0312 g/cm3. Of all gases, V. has the highest thermal conductivity, equal to 0.174 W / (m-K) at 0 ° C and 1 atm, i.e. 4.16-0-4 cal / (s-cm- ° C). The specific heat capacity of V. at 0 ° C and 1 atm Cp 14.208-103 j / (kg-K), i.e. 3.394 cal / (g- ° C). V. slightly soluble in water (0.0182 ml / g at 20 ° C and 1 atm), but well - in many metals (Ni, Pt, Pd, etc.), especially in palladium (850 volumes per 1 volume of Pd) . V.'s solubility in metals is associated with its ability to diffuse through them; diffusion through a carbonaceous alloy (for example, steel) is sometimes accompanied by the destruction of the alloy due to the interaction of steel with carbon (the so-called decarbonization). Liquid water is very light (density at -253°C 0.0708 g/cm3) and fluid (viscosity at -253°C 13.8 centigrade).
In most compounds, V. exhibits a valency (more precisely, an oxidation state) of +1, like sodium and other alkali metals; usually he is considered as an analogue of these metals, heading 1 gr. Mendeleev's systems. However, in metal hydrides, the B. ion is negatively charged (oxidation state -1), that is, the Na + H- hydride is built like Na + Cl- chloride. This and some other facts (the closeness of the physical properties of V. and halogens, the ability of halogens to replace V. in organic compounds) give reason to attribute V. also to group VII of the periodic system (for more details, see the Periodic system of elements). Under normal conditions, molecular V. is relatively inactive, combining directly with only the most active of the nonmetals (with fluorine, and in the light with chlorine). However, when heated, it reacts with many elements. Atomic V. has increased chemical activity compared to molecular V.. V. forms water with oxygen: H2 + 1 / 2O2 = H2O with the release of 285.937-103 J / mol, i.e. 68.3174 kcal / mol of heat (at 25 ° C and 1 atm). At ordinary temperatures, the reaction proceeds extremely slowly, above 550 ° C - with an explosion. The explosive limits of the hydrogen-oxygen mixture are (by volume) from 4 to 94% H2, and the hydrogen-air mixture - from 4 to 74% H2 (a mixture of 2 volumes of H2 and 1 volume of O2 is called explosive gas). V. is used to reduce many metals, as it takes away oxygen from their oxides:
CuO + H2 \u003d Cu + H2O,
Fe3O4 + 4H2 = 3Fe + 4H2O, etc.
V. forms hydrogen halides with halogens, for example:
H2 + Cl2 = 2HCl.
At the same time, it explodes with fluorine (even in the dark and at -252°C), reacts with chlorine and bromine only when illuminated or heated, and with iodine only when heated. V. interacts with nitrogen to form ammonia: 3H2 + N2 = 2NH3 only on a catalyst and at elevated temperatures and pressures. When heated, V. reacts vigorously with sulfur: H2 + S = H2S (hydrogen sulfide), much more difficult with selenium and tellurium. V. can react with pure carbon without a catalyst only at high temperatures: 2H2 + C (amorphous) = CH4 (methane). V. directly reacts with some metals (alkali, alkaline earth, etc.), forming hydrides: H2 + 2Li = 2LiH. Of great practical importance are the reactions of carbon monoxide with carbon monoxide, in which, depending on the temperature, pressure, and catalyst, various organic compounds are formed, such as HCHO, CH3OH, and others (see Carbon monoxide). Unsaturated hydrocarbons react with hydrogen, becoming saturated, for example: CnH2n + H2 = CnH2n+2 (see Hydrogenation).
The most common chemical element in the universe is hydrogen. This is a kind of reference point, because in the periodic table its atomic number is equal to one. Humanity hopes to be able to learn more about it as one of the most possible vehicles in the future. Hydrogen is the simplest, lightest, most common element, it is abundant everywhere - seventy-five percent of the total mass of matter. It is in any star, especially a lot of hydrogen in gas giants. Its role in stellar fusion reactions is key. Without hydrogen, there is no water, which means there is no life. Everyone remembers that a water molecule contains one oxygen atom, and two atoms in it are hydrogen. This is the well-known formula H 2 O.
How we use it
Hydrogen was discovered in 1766 by Henry Cavendish while analyzing the oxidation reaction of a metal. After several years of observation, he realized that in the process of burning hydrogen, water is formed. Previously, scientists isolated this element, but did not consider it independent. In 1783, hydrogen was given the name hydrogen (translated from the Greek "hydro" - water, and "gene" - to give birth). The element that generates water is hydrogen. It is a gas whose molecular formula is H 2 . If the temperature is close to room temperature and the pressure is normal, this element is imperceptible. Hydrogen can not even be caught by human senses - it is tasteless, colorless, odorless. But under pressure and at a temperature of -252.87 C (very cold!) This gas liquefies. This is how it is stored, since in the form of a gas it takes up much more space. It is liquid hydrogen that is used as rocket fuel.
Hydrogen can become solid, metallic, but for this, ultra-high pressure is needed, and this is what the most prominent scientists, physicists and chemists, are doing now. Already now this element serves as an alternative fuel for transport. Its application is similar to how an internal combustion engine works: when hydrogen is burned, a lot of its chemical energy is released. A method for creating a fuel cell based on it has also been practically developed: when combined with oxygen, a reaction occurs, and through this, water and electricity are formed. It is possible that transport will soon "switch" instead of gasoline to hydrogen - a lot of automakers are interested in creating alternative combustible materials, and there are some successes. But a purely hydrogen engine is still in the future, there are many difficulties. However, the advantages are such that the creation of a fuel tank with solid hydrogen is in full swing, and scientists and engineers are not going to retreat.
Basic information
Hydrogenium (lat.) - hydrogen, the first serial number in the periodic table, is designated H. The hydrogen atom has a mass of 1.0079, it is a gas that under normal conditions has no taste, no smell, no color. Chemists since the sixteenth century have described a certain combustible gas, denoting it in different ways. But it turned out for everyone under the same conditions - when acid acts on the metal. Hydrogen, even by Cavendish himself, for many years was simply called "combustible air." Only in 1783, Lavoisier proved that water has a complex composition, through synthesis and analysis, and four years later he gave "combustible air" its modern name. The root of this compound word is widely used when it is necessary to name hydrogen compounds and any processes in which it participates. For example, hydrogenation, hydride and the like. And the Russian name was proposed in 1824 by M. Solovyov.
In nature, the distribution of this element has no equal. In the lithosphere and hydrosphere of the earth's crust, its mass is one percent, but hydrogen atoms are as much as sixteen percent. The most common water on Earth, and 11.19% by weight in it is hydrogen. Also, it is certainly present in almost all compounds that make up oil, coal, all natural gases, clay. There is hydrogen in all organisms of plants and animals - in the composition of proteins, fats, nucleic acids, carbohydrates, and so on. The free state for hydrogen is not typical and almost never occurs - there is very little of it in natural and volcanic gases. A very negligible amount of hydrogen in the atmosphere - 0.0001%, in terms of the number of atoms. On the other hand, whole streams of protons represent hydrogen in the near-Earth space, which makes up the inner radiation belt of our planet.
Space
In space, no element is as common as hydrogen. The volume of hydrogen in the composition of the elements of the Sun is more than half of its mass. Most stars form hydrogen in the form of plasma. The main part of various gases of nebulae and the interstellar medium also consists of hydrogen. It is present in comets, in the atmosphere of a number of planets. Naturally, not in its pure form, either as free H 2, or as methane CH 4, or as ammonia NH 3, even as water H 2 O. Very often there are radicals CH, NH, SiN, OH, PH and the like. As a stream of protons, hydrogen is part of the corpuscular solar radiation and cosmic rays.
In ordinary hydrogen, a mixture of two stable isotopes is light hydrogen (or protium 1 H) and heavy hydrogen (or deuterium - 2 H or D). There are other isotopes: radioactive tritium - 3 H or T, otherwise - superheavy hydrogen. And also very unstable 4 N. In nature, a hydrogen compound contains isotopes in such proportions: there are 6800 protium atoms per deuterium atom. Tritium is formed in the atmosphere from nitrogen, which is affected by cosmic ray neutrons, but negligible. What do the mass numbers of isotopes mean? The number indicates that the protium nucleus has only one proton, while deuterium has not only a proton, but also a neutron in the nucleus of an atom. Tritium has two neutrons in the nucleus for one proton. But 4 N contains three neutrons per proton. Therefore, the physical and chemical properties of hydrogen isotopes are very different compared to the isotopes of all other elements - the mass difference is too large.
Structure and physical properties
In terms of structure, the hydrogen atom is the simplest in comparison with all other elements: one nucleus - one electron. Ionization potential - the binding energy of the nucleus with the electron - 13.595 electron volts (eV). It is precisely because of the simplicity of this structure that the hydrogen atom is a convenient model in quantum mechanics when it is necessary to calculate the energy levels of more complex atoms. In the H 2 molecule, there are two atoms that are connected by a chemical covalent bond. The decay energy is very high. Atomic hydrogen can be formed in chemical reactions, such as zinc and hydrochloric acid. However, interaction with hydrogen practically does not occur - the atomic state of hydrogen is very short, the atoms immediately recombine into H 2 molecules.
From a physical point of view, hydrogen is lighter than all known substances - more than fourteen times lighter than air (remember flying balloons on holidays - they have just hydrogen inside). However, helium can boil, liquefy, melt, solidify, and only helium boils and melts at lower temperatures. It is difficult to liquefy it, you need a temperature below -240 degrees Celsius. But it has a very high thermal conductivity. It almost does not dissolve in water, but metal interacts perfectly with hydrogen - it dissolves in almost all, best of all in palladium (850 volumes are spent on one volume of hydrogen). Liquid hydrogen is light and fluid, and when dissolved in metals, it often destroys alloys due to interaction with carbon (steel, for example), diffusion, decarbonization occurs.
Chemical properties
In compounds, for the most part, hydrogen shows an oxidation state (valence) of +1, like sodium and other alkali metals. He is considered as their analogue, standing at the head of the first group of the Mendeleev system. But the hydrogen ion in metal hydrides is negatively charged, with an oxidation state of -1. Also, this element is close to halogens, which are even able to replace it in organic compounds. This means that hydrogen can also be attributed to the seventh group of the Mendeleev system. Under normal conditions, hydrogen molecules do not differ in activity, combining only with the most active non-metals: it is good with fluorine, and if it is light, with chlorine. But when heated, hydrogen becomes different - it reacts with many elements. Atomic hydrogen, compared to molecular hydrogen, is very active chemically, so water is formed in connection with oxygen, and energy and heat are released along the way. At room temperature, this reaction is very slow, but when heated above five hundred and fifty degrees, an explosion is obtained.
Hydrogen is used to reduce metals, because it takes away oxygen from their oxides. With fluorine, hydrogen forms an explosion even in the dark and at minus two hundred and fifty-two degrees Celsius. Chlorine and bromine excite hydrogen only when heated or illuminated, and iodine only when heated. Hydrogen and nitrogen form ammonia (this is how most fertilizers are made). When heated, it very actively interacts with sulfur, and hydrogen sulfide is obtained. With tellurium and selenium it is difficult to cause a reaction of hydrogen, but with pure carbon the reaction occurs at very high temperatures, and methane is obtained. With carbon monoxide, hydrogen forms various organic compounds, pressure, temperature, catalysts influence here, and all this is of great practical importance. In general, the role of hydrogen, as well as its compounds, is exceptionally great, since it gives acidic properties to protic acids. Hydrogen bonds are formed with many elements, affecting the properties of both inorganic and organic compounds.
Getting and using
Hydrogen is obtained on an industrial scale from natural gases - combustible, coke oven, oil refining gases. It can also be obtained by electrolysis where electricity is not too expensive. However, the most important method of hydrogen production is the catalytic reaction of hydrocarbons, mostly methane, with water vapor, when conversion is obtained. The method of oxidizing hydrocarbons with oxygen is also widely used. Extraction of hydrogen from natural gas is the cheapest way. The other two are the use of coke oven gas and refinery gas - hydrogen is released when the other components are liquefied. They are more easily liquefied, and for hydrogen, as we remember, you need -252 degrees.
Hydrogen peroxide is very popular. Treatment with this solution is used very often. The molecular formula H 2 O 2 is unlikely to be named by all those millions of people who want to be blondes and lighten their hair, as well as those who love cleanliness in the kitchen. Even those who treat scratches from playing with a kitten often do not realize that they are using hydrogen treatment. But everyone knows the story: since 1852, hydrogen has been used in aeronautics for a long time. The airship invented by Henry Giffard was based on hydrogen. They were called zeppelins. The zeppelins were forced out of the sky by the rapid development of aircraft construction. In 1937, there was a major accident when the Hindenburg airship burned down. After this incident, zeppelins were never used again. But at the end of the eighteenth century, the distribution of balloons filled with hydrogen was ubiquitous. In addition to the production of ammonia, today hydrogen is needed for the manufacture of methyl alcohol and other alcohols, gasoline, hydrogenated heavy fuel oil and solid fuels. You can not do without hydrogen when welding, when cutting metals - it can be oxygen-hydrogen and atomic-hydrogen. And tritium and deuterium give life to nuclear energy. This, as we remember, isotopes of hydrogen.
Neumyvakin
Hydrogen as a chemical element is so good that it could not help but have its own fans. Ivan Pavlovich Neumyvakin - doctor of medical sciences, professor, laureate of the State Prize and many more titles and awards, among them. As a doctor of traditional medicine, he was named the best folk healer in Russia. It was he who developed many methods and principles of providing medical care to astronauts in flight. It was he who created a unique hospital - a hospital on board a space ship. At the same time he was the state coordinator of the direction of cosmetic medicine. Space and cosmetics. His passion for hydrogen is not aimed at making big money, as is now the case in domestic medicine, but on the contrary, to teach people how to cure anything from literally a penny remedy, without additional visits to pharmacies.
He promotes treatment with a drug that is present in literally every home. This is hydrogen peroxide. You can criticize Neumyvakin as much as you like, he will still insist on his own: yes, indeed, literally everything can be cured with hydrogen peroxide, because it saturates the internal cells of the body with oxygen, destroys toxins, normalizes acid and alkaline balance, and from here tissues are regenerated, the entire body is rejuvenated. organism. No one has yet seen anyone cured with hydrogen peroxide, much less examined, but Neumyvakin claims that using this remedy, you can completely get rid of viral, bacterial and fungal diseases, prevent the development of tumors and atherosclerosis, defeat depression, rejuvenate the body and never get sick SARS and colds.
Panacea
Ivan Pavlovich is sure that with the proper use of this simple drug and with all the simple instructions, you can defeat many diseases, including very serious ones. Their list is huge: from periodontal disease and tonsillitis to myocardial infarction, stroke and diabetes. Such trifles as sinusitis or osteochondrosis fly away from the first treatment sessions. Even cancerous tumors are frightened and run away from hydrogen peroxide, because the immune system is stimulated, the life of the body and its defenses are activated.
Even children can be treated in this way, except that it is better for pregnant women to refrain from using hydrogen peroxide for the time being. This method is also not recommended for people with transplanted organs due to possible tissue incompatibility. The dosage should be strictly observed: from one drop to ten, adding one every day. Three times a day (thirty drops of a three percent solution of hydrogen peroxide per day, wow!) half an hour before meals. You can enter the solution intravenously and under the supervision of a physician. Sometimes hydrogen peroxide is combined for a more effective effect with other drugs. Inside the solution is used only in diluted form - with clean water.
Outwardly
Compresses and rinses were very popular even before Professor Neumyvakin created his methods. Everyone knows that, like alcohol compresses, hydrogen peroxide cannot be used in its pure form, because tissue burns will result, but warts or fungal infections are lubricated locally and with a strong solution - up to fifteen percent.
With skin rashes, with headaches, procedures are also performed in which hydrogen peroxide is involved. The compress should be done with a cotton cloth soaked in a solution of two teaspoons of three percent hydrogen peroxide and fifty milligrams of pure water. Cover the fabric with foil and wrap with wool or a towel. The duration of the compress is from a quarter of an hour to an hour and a half in the morning and evening until recovery.
Doctors' opinion
Opinions are divided, not everyone admires the properties of hydrogen peroxide, moreover, they not only do not believe them, they laugh at them. Among the doctors there are those who supported Neumyvakin and even picked up the development of his theory, but they are in the minority. Most doctors consider such a treatment plan not only ineffective, but often fatal.
Indeed, there is not yet officially a single proven case when a patient would be cured with hydrogen peroxide. At the same time, there is no information about the deterioration of health in connection with the use of this method. But precious time is lost, and a person who has received one of the serious diseases and completely relied on Neumyvakin's panacea runs the risk of being late for the start of his real traditional treatment.
Hydrogen is a chemical element with symbol H and atomic number 1. With a standard atomic weight of about 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical in the universe, accounting for approximately 75% of the total mass of a baryon. Stars are mostly composed of hydrogen in the plasma state. The most common isotope of hydrogen, called protium (this name is rarely used, symbol 1H), has one proton and no neutrons. The widespread appearance of atomic hydrogen first occurred in the era of recombination. At standard temperatures and pressures, hydrogen is a colorless, odorless, tasteless, non-toxic, non-metallic, flammable diatomic gas with the molecular formula H2. Since hydrogen readily forms covalent bonds with most non-metallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays a particularly important role in acid-base reactions because most acid-based reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a negative charge (i.e., anion) and is known as a hydride, or as a positively charged (i.e., cation) species, denoted by the symbol H+. The hydrogen cation is described as being made up of a simple proton, but the actual hydrogen cations in ionic compounds are always more complex. As the only neutral atom for which the Schrödinger equation can be solved analytically, hydrogen (namely, the study of the energy and binding of its atom) has played a key role in the development of quantum mechanics. Hydrogen gas was first produced artificially in the early 16th century by the reaction of acids with metals. In 1766-81. Henry Cavendish was the first to recognize that hydrogen gas is a discrete substance, and that it produces water when burned, hence its name: hydrogen in Greek means "water producer". The industrial production of hydrogen is mainly associated with the steam conversion of natural gas and, less frequently, with more energy-intensive methods such as water electrolysis. Most hydrogen is used near where it is produced, with the two most common uses being fossil fuel processing (eg hydrocracking) and ammonia production, mainly for the fertilizer market. Hydrogen is a concern in metallurgy because it can brittle many metals, making it difficult to design pipelines and storage tanks.
Properties
Combustion
Hydrogen gas (dihydrogen or molecular hydrogen) is a flammable gas that will burn in air over a very wide range of concentrations from 4% to 75% by volume. The enthalpy of combustion is 286 kJ/mol:
2 H2 (g) + O2 (g) → 2 H2O (l) + 572 kJ (286 kJ/mol)
Hydrogen gas forms explosive mixtures with air in concentrations from 4-74% and with chlorine in concentrations up to 5.95%. Explosive reactions can be caused by sparks, heat or sunlight. The autoignition temperature of hydrogen, the spontaneous ignition temperature in air, is 500 °C (932 °F) . Pure hydrogen-oxygen flames emit ultraviolet radiation and with a high oxygen mixture are almost invisible to the naked eye, as evidenced by the faint plume of the Space Shuttle main engine compared to the highly visible plume of the Space Shuttle solid rocket booster, which uses an ammonium perchlorate composite. A flame detector may be required to detect a leak of burning hydrogen; such leaks can be very dangerous. Hydrogen flame under other conditions is blue, and resembles the blue flame of natural gas. The sinking of the airship "Hindenburg" is a notorious example of hydrogen burning, and the case is still under discussion. The visible orange flame in this incident was caused by exposure to a mixture of hydrogen and oxygen combined with carbon compounds from the airship's skin. H2 reacts with every oxidizing element. Hydrogen can react spontaneously at room temperature with chlorine and fluorine to form the corresponding hydrogen halides, hydrogen chloride and hydrogen fluoride, which are also potentially hazardous acids.
Electron energy levels
The ground state energy level of an electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon with a wavelength of about 91 nm. The energy levels of hydrogen can be calculated quite accurately using the Bohr model of the atom, which conceptualizes the electron as an "orbital" proton, similar to the Earth's orbit of the Sun. However, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held together by gravity. Due to the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in Bohr's model can only occupy certain allowable distances from the proton, and thus only certain allowable energies. A more accurate description of the hydrogen atom comes from a purely quantum mechanical treatment that uses the Schrödinger equation, the Dirac equation, or even the Feynman integrated circuit to compute the probability density distribution of an electron around a proton. The most complex processing methods allow one to obtain small effects of special relativity and vacuum polarization. In quantum machining, the electron in the ground state hydrogen atom has no torque at all, illustrating how a "planetary orbit" differs from the motion of an electron.
Elementary molecular forms
There are two different spin isomers of diatomic hydrogen molecules that differ in the relative spin of their nuclei. In the orthohydrogen form, the spins of the two protons are parallel and form a triplet state with a molecular spin quantum number of 1 (1/2 + 1/2); in the parahydrogen form, the spins are antiparallel and form a singlet with a molecular spin quantum number of 0 (1/2 1/2). At standard temperature and pressure, hydrogen gas contains about 25% of the para form and 75% of the ortho form, also known as the "normal form". The equilibrium ratio of orthohydrogen to parahydrogen depends on temperature, but because the ortho form is an excited state and has a higher energy than the para form, it is unstable and cannot be purified. At very low temperatures, the equilibrium state consists almost exclusively of the para form. The thermal properties of the liquid and gas phases of pure parahydrogen differ significantly from those of the normal form due to differences in rotational heat capacities, which is discussed in more detail in hydrogen spin isomers. The ortho/pair difference also occurs in other hydrogen-containing molecules or functional groups such as water and methylene, but this is of little significance for their thermal properties. The uncatalyzed interconversion between para and ortho H2 increases with increasing temperature; thus rapidly condensed H2 contains large amounts of the high energy orthogonal form, which is very slowly converted to the para form. The ortho/para ratio in condensed H2 is an important factor in the preparation and storage of liquid hydrogen: the conversion from ortho to para is exothermic and provides enough heat to vaporize some of the hydrogen liquid, resulting in the loss of liquefied material. Catalysts for ortho-para conversion such as iron oxide, activated carbon, platinized asbestos, rare earths, uranium compounds, chromium oxide or some nickel compounds are used in hydrogen cooling.
Phases
Hydrogen gas
liquid hydrogen
sludge hydrogen
solid hydrogen
metallic hydrogen
Connections
Covalent and organic compounds
While H2 is not very reactive under standard conditions, it forms compounds with most elements. Hydrogen can form compounds with elements that are more electronegative, such as halogens (eg F, Cl, Br, I) or oxygen; in these compounds, the hydrogen takes on a partial positive charge. When bonded to fluorine, oxygen, or nitrogen, hydrogen can participate in the form of a medium-strength non-covalent bond with the hydrogen of other similar molecules, a phenomenon called hydrogen bonding, which is critical to the stability of many biological molecules. Hydrogen also forms compounds with less electronegative elements such as metals and metalloids, where it takes on a partial negative charge. These compounds are often known as hydrides. Hydrogen forms a wide variety of compounds with carbon, called hydrocarbons, and an even greater variety of compounds with heteroatoms, which, because of their common association with living things, are called organic compounds. The study of their properties is the concern of organic chemistry, and their study in the context of living organisms is known as biochemistry. By some definitions, "organic" compounds must contain only carbon. However, most also contain hydrogen, and since it is the carbon-hydrogen bond that gives this class of compounds much of their specific chemical characteristics, carbon-hydrogen bonds are required in some definitions of the word "organic" in chemistry. Millions of hydrocarbons are known, and they are usually formed by complex synthetic pathways that rarely involve elemental hydrogen.
hydrides
Hydrogen compounds are often called hydrides. The term "hydride" suggests that the H atom has acquired a negative or anionic character, designated H-, and is used when hydrogen forms a compound with a more electropositive element. The existence of a hydride anion, proposed by Gilbert N. Lewis in 1916 for group 1 and 2 salt-containing hydrides, was demonstrated by Moers in 1920 by electrolysis of molten lithium hydride (LiH), producing a stoichiometric amount of hydrogen per anode. For hydrides other than group 1 and 2 metals, the term is misleading given the low electronegativity of hydrogen. An exception in group 2 hydrides is BeH2, which is polymeric. In lithium aluminum hydride, the AlH-4 anion carries hydride centers firmly attached to Al(III). Although hydrides can form in almost all main group elements, the number and combination of possible compounds vary greatly; for example, over 100 binary borane hydrides and only one binary aluminum hydride are known. Binary indium hydride has not yet been identified, although large complexes exist. In inorganic chemistry, hydrides can also serve as bridging ligands that link two metal centers in a coordination complex. This function is especially characteristic of group 13 elements, especially in boranes (boron hydrides) and aluminum complexes, as well as in clustered carboranes.
Protons and acids
Oxidation of hydrogen removes its electron and gives H+, which contains no electrons and no nucleus, which usually consists of a single proton. This is why H+ is often referred to as a proton. This view is central to the discussion of acids. According to the Bronsted-Lowry theory, acids are proton donors and bases are proton acceptors. The naked proton, H+, cannot exist in solution or in ionic crystals because of its irresistible attraction to other atoms or molecules with electrons. Except for the high temperatures associated with plasmas, such protons cannot be removed from the electron clouds of atoms and molecules and will remain attached to them. However, the term "proton" is sometimes used metaphorically to refer to positively charged or cationic hydrogen attached to other species in this manner, and as such is designated "H+" without any meaning that any individual protons exist freely as a species. To avoid the appearance of a naked "solvated proton" in solution, acidic aqueous solutions are sometimes thought to contain a less unlikely fictitious species called the "hydronium ion" (H 3 O+). However, even in this case, such solvated hydrogen cations are more realistically perceived as organized clusters that form species close to H 9O+4. Other oxonium ions are found when water is in an acidic solution with other solvents. Despite being exotic on Earth, one of the most common ions in the universe is H+3, known as protonated molecular hydrogen or the trihydrogen cation.
isotopes
Hydrogen has three naturally occurring isotopes, designated 1H, 2H, and 3H. Other highly unstable nuclei (4H to 7H) have been synthesized in the laboratory but have not been observed in nature. 1H is the most common isotope of hydrogen, with an abundance of over 99.98%. Since the nucleus of this isotope consists of only one proton, it is given the descriptive but rarely used formal name protium. 2H, the other stable isotope of hydrogen, is known as deuterium and contains one proton and one neutron in the nucleus. It is believed that all the deuterium in the universe was produced during the Big Bang and has existed since that time until now. Deuterium is not a radioactive element and does not pose a significant toxicity hazard. Water enriched in molecules that include deuterium instead of normal hydrogen is called heavy water. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for 1H-NMR spectroscopy. Heavy water is used as a neutron moderator and coolant for nuclear reactors. Deuterium is also a potential fuel for commercial nuclear fusion. 3H is known as tritium and contains one proton and two neutrons in the nucleus. It is radioactive, decaying into helium-3 via beta decay with a half-life of 12.32 years. It is so radioactive that it can be used in luminous paint, making it useful in making watches with luminous dials, for example. The glass prevents a small amount of radiation from escaping. A small amount of tritium is produced naturally by the interaction of cosmic rays with atmospheric gases; tritium has also been released during nuclear weapons testing. It is used in nuclear fusion reactions as an indicator of isotope geochemistry and in specialized self-powered lighting devices. Tritium has also been used in chemical and biological labeling experiments as a radioactive label. Hydrogen is the only element that has different names for its isotopes that are in common use today. During the early study of radioactivity, various heavy radioactive isotopes were given their own names, but such names are no longer used, with the exception of deuterium and tritium. The symbols D and T (instead of 2H and 3H) are sometimes used for deuterium and tritium, but the corresponding symbol for protium P is already used for phosphorus and thus not available for protium. In its nomenclature guidelines, the International Union of Pure and Applied Chemistry allows any of the symbols from D, T, 2H, and 3H to be used, although 2H and 3H are preferred. The exotic atom muonium (symbol Mu), consisting of an antimuon and an electron, is also sometimes considered a light radioisotope of hydrogen due to the mass difference between the antimuon and the electron, which was discovered in 1960. During the lifetime of the muon, 2.2 μs, muonium can enter compounds such as muonium chloride (MuCl) or sodium muonide (NaMu), similarly to hydrogen chloride and sodium hydride, respectively.
Story
Discovery and use
In 1671, Robert Boyle discovered and described the reaction between iron filings and dilute acids that results in hydrogen gas. In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, naming the gas "flammable air" because of the metal-acid reaction. He suggested that "flammable air" was in fact identical to a hypothetical substance called "phlogiston" and found again in 1781 that the gas produced water when burned. It is believed that it was he who discovered hydrogen as an element. In 1783, Antoine Lavoisier gave the element the name hydrogen (from the Greek ὑδρο-hydro meaning "water" and -γενής genes meaning "creator") when he and Laplace reproduced Cavendish's data that water was formed when hydrogen was burned. Lavoisier produced hydrogen for his conservation of mass experiments by reacting a stream of steam with metallic iron through an incandescent lamp heated in a fire. The anaerobic oxidation of iron by water protons at high temperature can be schematically represented by a set of the following reactions:
Fe + H2O → FeO + H2
2 Fe + 3 H2O → Fe2O3 + 3 H2
3 Fe + 4 H2O → Fe3O4 + 4 H2
Many metals, such as zirconium, undergo a similar reaction with water to produce hydrogen. Hydrogen was first liquefied by James Dewar in 1898 using regenerative refrigeration and his invention, the vacuum flask. The following year, he produced solid hydrogen. Deuterium was discovered in December 1931 by Harold Uray and tritium was prepared in 1934 by Ernest Rutherford, Mark Oliphant and Paul Harteck. Heavy water, which is made up of deuterium instead of ordinary hydrogen, was discovered by Yurey's group in 1932. François Isaac de Rivaz built the first "Rivaz" engine, an internal combustion engine powered by hydrogen and oxygen, in 1806. Edward Daniel Clark invented the hydrogen gas tube in 1819. Döbereiner's steel (the first full-fledged lighter) was invented in 1823. The first hydrogen balloon was invented by Jacques Charles in 1783. Hydrogen provided the rise of the first reliable form of air traffic after Henri Giffard's invention of the first hydrogen-lifted airship in 1852. The German Count Ferdinand von Zeppelin promoted the idea of rigid airships lifted into the air by hydrogen, which were later called Zeppelins; the first of these flew for the first time in 1900. Regularly scheduled flights began in 1910 and by the outbreak of World War I in August 1914 they had carried 35,000 passengers without major incident. During the war, hydrogen airships were used as observation platforms and bombers. The first non-stop transatlantic flight was made by the British airship R34 in 1919. Regular passenger service resumed in the 1920s and the discovery of helium reserves in the United States was supposed to improve aviation safety, but the US government refused to sell gas for this purpose, so H2 was used in the Hindenburg airship, which was destroyed in the Milan fire in New Jersey May 6, 1937. The incident was broadcast live on the radio and videotaped. It was widely assumed that the cause of the ignition was a hydrogen leak, however subsequent studies indicate that the aluminized fabric coating was ignited by static electricity. But by this time, hydrogen's reputation as a lifting gas had already been damaged. That same year, the first hydrogen-cooled turbogenerator with hydrogen gas as the coolant in the rotor and stator went into operation in 1937 in Dayton, Ohio, by the Dayton Power & Light Co.; due to the thermal conductivity of hydrogen gas, it is the most common gas for use in this field today. The nickel-hydrogen battery was first used in 1977 aboard the US Navigation Technology Satellite 2 (NTS-2). The ISS, Mars Odyssey and Mars Global Surveyor are equipped with nickel-hydrogen batteries. In the dark part of its orbit, the Hubble Space Telescope is also powered by nickel-hydrogen batteries, which were finally replaced in May 2009, more than 19 years after launch and 13 years after they were designed.
Role in quantum theory
Because of its simple atomic structure of only a proton and an electron, the hydrogen atom, along with the spectrum of light created from or absorbed by it, has been central to the development of atomic structure theory. In addition, the study of the corresponding simplicity of the hydrogen molecule and the corresponding H+2 cation led to an understanding of the nature of the chemical bond, which soon followed the physical treatment of the hydrogen atom in quantum mechanics in mid-2020. One of the first quantum effects that was clearly observed (but not understood at that time) was Maxwell's observation involving hydrogen half a century before there was a full quantum mechanical theory. Maxwell noted that the specific heat capacity of H2 irreversibly departs from a diatomic gas below room temperature and begins to more and more resemble the specific heat capacity of a monatomic gas at cryogenic temperatures. According to quantum theory, this behavior arises from the spacing of (quantized) rotational energy levels, which are especially widely spaced in H2 due to its low mass. These widely spaced levels prevent an equal division of thermal energy into rotational motion in hydrogen at low temperatures. Diatom gases, which are composed of heavier atoms, do not have such widely spaced levels and do not exhibit the same effect. Antihydrogen is the antimaterial analogue of hydrogen. It consists of an antiproton with a positron. Antihydrogen is the only type of antimatter atom that has been obtained as of 2015.
Being in nature
Hydrogen is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms. (Most of the mass of the universe, however, is not in the form of this chemical element, but is thought to have as yet undiscovered mass forms such as dark matter and dark energy.) This element is found in great abundance in stars and gas giants. H2 molecular clouds are associated with star formation. Hydrogen plays a vital role in turning stars on through the proton-proton reaction and nuclear fusion of the CNO cycle. Throughout the world, hydrogen occurs mainly in atomic and plasma states with properties quite different from those of molecular hydrogen. As a plasma, the electron and proton of hydrogen are not bound to each other, resulting in very high electrical conductivity and high emissivity (generating light from the Sun and other stars). Charged particles are strongly affected by magnetic and electric fields. For example, in the solar wind, they interact with the Earth's magnetosphere, creating Birkeland currents and the aurora. Hydrogen is in a neutral atomic state in the interstellar medium. The large amount of neutral hydrogen found in evanescent Liman-alpha systems is believed to dominate the cosmological baryon density of the Universe up to redshift z = 4. Under normal conditions on Earth, elemental hydrogen exists as a diatomic gas, H2. However, hydrogen gas is very rare in the earth's atmosphere (1 ppm by volume) due to its light weight, which allows it to defy the earth's gravity more easily than heavier gases. However, hydrogen is the third most abundant element on the Earth's surface, existing primarily in the form of chemical compounds such as hydrocarbons and water. Hydrogen gas is produced by some bacteria and algae and is a natural component of the flute, as is methane, which is an increasingly important source of hydrogen. A molecular form called protonated molecular hydrogen (H+3) is found in the interstellar medium, where it is generated by the ionization of molecular hydrogen from cosmic rays. This charged ion has also been observed in the upper atmosphere of the planet Jupiter. The ion is relatively stable in the environment due to its low temperature and density. H+3 is one of the most abundant ions in the universe and plays a prominent role in the chemistry of the interstellar medium. Neutral triatomic hydrogen H3 can exist only in an excited form and is unstable. In contrast, the positive molecular hydrogen ion (H+2) is a rare molecule in the universe.
Hydrogen production
H2 is produced in chemical and biological laboratories, often as a by-product of other reactions; in industry for the hydrogenation of unsaturated substrates; and in nature as a means of displacing reducing equivalents in biochemical reactions.
Steam reforming
Hydrogen can be produced in several ways, but economically the most important processes involve the removal of hydrogen from hydrocarbons, as about 95% of hydrogen production in 2000 came from steam reforming. Commercially, large volumes of hydrogen are usually produced by steam reforming of natural gas. At high temperatures (1000-1400 K, 700-1100 °C or 1300-2000 °F) steam (steam) reacts with methane to produce carbon monoxide and H2.
CH4 + H2O → CO + 3 H2
This reaction works best at low pressures, but can still be carried out at high pressures (2.0 MPa, 20 atm, or 600 inHg). This is because high pressure H2 is the most popular product and pressurized superheat cleaning systems perform better at higher pressures. The product mixture is known as "synthesis gas" because it is often used directly to produce methanol and related compounds. Hydrocarbons other than methane can be used to produce synthesis gas with various product ratios. One of the many complications of this highly optimized technology is the formation of coke or carbon:
CH4 → C + 2 H2
Therefore, steam reforming usually uses an excess of H2O. Additional hydrogen can be recovered from the steam using carbon monoxide through a water gas shift reaction, especially using an iron oxide catalyst. This reaction is also a common industrial source of carbon dioxide:
CO + H2O → CO2 + H2
Other important methods for H2 include the partial oxidation of hydrocarbons:
2 CH4 + O2 → 2 CO + 4 H2
And the coal reaction, which can serve as a prelude to the shift reaction described above:
C + H2O → CO + H2
Sometimes hydrogen is produced and consumed in the same industrial process, without separation. In the Haber process for the production of ammonia, hydrogen is generated from natural gas. Salt solution electrolysis to produce chlorine also produces hydrogen as a by-product.
metallic acid
In the laboratory, H2 is usually made by reacting dilute non-oxidizing acids with certain reactive metals such as zinc with a Kipp apparatus.
Zn + 2 H + → Zn2 + + H2
Aluminum can also produce H2 when treated with bases:
2 Al + 6 H2O + 2 OH- → 2 Al (OH) -4 + 3 H2
Water electrolysis is a simple way to produce hydrogen. A low voltage current flows through the water and oxygen gas is generated at the anode while hydrogen gas is generated at the cathode. Typically, the cathode is made from platinum or another inert metal in the production of hydrogen for storage. If, however, the gas is to be burned in situ, the presence of oxygen is desirable to promote combustion, and therefore both electrodes will be made of inert metals. (For example, iron oxidizes and therefore reduces the amount of oxygen released). The theoretical maximum efficiency (electricity used in relation to the energy value of hydrogen produced) is in the range of 80-94%.
2 H2O (L) → 2 H2 (g) + O2 (g)
An alloy of aluminum and gallium in the form of granules added to water can be used to produce hydrogen. This process also produces alumina, but the expensive gallium, which prevents oxide skin from forming on the pellets, can be reused. This has important potential implications for the economics of hydrogen, since hydrogen can be produced locally and does not need to be transported.
Thermochemical properties
There are more than 200 thermochemical cycles that can be used to separate water, about a dozen of these cycles, such as the iron oxide cycle, the cerium (IV) oxide cycle, the cerium (III) oxide cycle, the zinc-zinc oxide cycle, the sulfur iodine cycle, the copper cycle, and chlorine and sulfur hybrid cycle are under research and testing to produce hydrogen and oxygen from water and heat without the use of electricity. A number of laboratories (including those in France, Germany, Greece, Japan and the USA) are developing thermochemical methods for producing hydrogen from solar energy and water.
Anaerobic corrosion
Under anaerobic conditions, iron and steel alloys are slowly oxidized by water protons while being reduced in molecular hydrogen (H2). Anaerobic corrosion of iron leads first to the formation of iron hydroxide (green rust) and can be described by the following reaction: Fe + 2 H2O → Fe (OH) 2 + H2. In turn, under anaerobic conditions, iron hydroxide (Fe (OH) 2) can be oxidized by water protons to form magnetite and molecular hydrogen. This process is described by the Shikorra reaction: 3 Fe (OH) 2 → Fe3O4 + 2 H2O + H2 iron hydroxide → magnesium + water + hydrogen. Well-crystallized magnetite (Fe3O4) is thermodynamically more stable than iron hydroxide (Fe(OH)2). This process occurs during anaerobic corrosion of iron and steel in anoxic groundwater and when soils are reclaimed below the water table.
Geological origin: serpentinization reaction
In the absence of oxygen (O2) in deep geological conditions prevailing far from the Earth's atmosphere, hydrogen (H2) is formed during serpentinization by anaerobic oxidation by water protons (H+) of iron silicate (Fe2+) present in the crystal lattice of fayalite (Fe2SiO4, minal olivine -gland). The corresponding reaction leading to the formation of magnetite (Fe3O4), quartz (SiO2) and hydrogen (H2): 3Fe2SiO4 + 2 H2O → 2 Fe3O4 + 3 SiO2 + 3 H2 fayalite + water → magnetite + quartz + hydrogen. This reaction closely resembles the Shikorra reaction observed in the anaerobic oxidation of iron hydroxide in contact with water.
Formation in transformers
Of all the hazardous gases produced in power transformers, hydrogen is the most common and is generated in the majority of faults; thus, the formation of hydrogen is an early sign of serious problems in the life cycle of a transformer.
Applications
Consumption in various processes
Large quantities of H2 are needed in the petroleum and chemical industries. The greatest use of H2 is for the processing (“upgrading”) of fossil fuels and for the production of ammonia. In petrochemical plants, H2 is used in hydrodealkylation, hydrodesulfurization and hydrocracking. H2 has several other important uses. H2 is used as a hydrogenating agent, in particular to increase the saturation level of unsaturated fats and oils (found in items such as margarine), and in methanol production. It is also a source of hydrogen in the production of hydrochloric acid. H2 is also used as a reducing agent for metal ores. Hydrogen is highly soluble in many rare earth and transition metals and is soluble in both nanocrystalline and amorphous metals. The solubility of hydrogen in metals depends on local distortions or impurities in the crystal lattice. This can be useful when hydrogen is purified by passing through hot palladium disks, but the high solubility of the gas is a metallurgical problem that embrittles many metals, making piping and storage tanks difficult to design. In addition to being used as a reagent, H2 has a wide range of applications in physics and engineering. It is used as a shielding gas in welding methods such as atomic hydrogen welding. H2 is used as a rotor coolant in electrical generators in power plants because it has the highest thermal conductivity of any gas. Liquid H2 is used in cryogenic research, including research into superconductivity. Because H2 is lighter than air, at just over 1/14 the density of air, it was once widely used as a lifting gas in balloons and airships. In newer applications, hydrogen is used neat or mixed with nitrogen (sometimes called forming gas) as a tracer gas for instant leak detection. Hydrogen is used in the automotive, chemical, energy, aerospace and telecommunications industries. Hydrogen is a permitted food additive (E 949) that allows food leak testing, among other antioxidant properties. Rare isotopes of hydrogen also have specific uses. Deuterium (hydrogen-2) is used in nuclear fission applications as a slow neutron moderator and in nuclear fusion reactions. Deuterium compounds are used in the field of chemistry and biology in the study of the isotope effects of the reaction. Tritium (hydrogen-3), produced in nuclear reactors, is used in the manufacture of hydrogen bombs, as an isotope marker in the biological sciences, and as a radiation source in luminous paints. The triple point temperature of equilibrium hydrogen is the defining fixed point on the ITS-90 temperature scale at 13.8033 Kelvin.
Cooling medium
Hydrogen is commonly used in power plants as a refrigerant in generators due to a number of favorable properties that are a direct result of its light diatomic molecules. These include low density, low viscosity, and the highest specific heat capacity and thermal conductivity of any gas.
Energy carrier
Hydrogen is not an energy resource, except in the hypothetical context of commercial fusion power plants using deuterium or tritium, a technology currently far from mature. The energy of the Sun comes from the nuclear fusion of hydrogen, but this process is difficult to achieve on Earth. Elemental hydrogen from solar, biological or electrical sources requires more energy to produce it than it takes to burn it, so in these cases the hydrogen functions as an energy carrier, similar to a battery. Hydrogen can be obtained from fossil sources (such as methane), but these sources are exhaustible. The energy density per unit volume of both liquid hydrogen and compressed gaseous hydrogen at any practically achievable pressure is significantly less than conventional energy sources, although the energy density per unit mass of fuel is higher. However, elemental hydrogen has been widely discussed in the energy context as a possible future economy-wide energy carrier. For example, CO2 sequestration followed by carbon capture and storage could be done at the point of production of H2 from fossil fuels. Hydrogen used in transport will burn relatively cleanly, with some NOx emissions but no carbon emissions. However, the infrastructure cost associated with a full conversion to a hydrogen economy will be significant. Fuel cells can turn hydrogen and oxygen directly into electricity more efficiently than internal combustion engines.
semiconductor industry
Hydrogen is used to saturate the dangling bonds of amorphous silicon and amorphous carbon, which helps to stabilize the properties of the material. It is also a potential electron donor in various oxide materials including ZnO, SnO2, CdO, MgO, ZrO2, HfO2, La2O3, Y2O3, TiO2, SrTiO3, LaAlO3, SiO2, Al2O3, ZrSiO4, HfSiO4, and SrZrO3.
biological reactions
H2 is a product of some types of anaerobic metabolism and is produced by several microorganisms, usually through reactions catalyzed by iron- or nickel-containing enzymes called hydrogenases. These enzymes catalyze a reversible redox reaction between H2 and its two protons and two electrons components. The creation of hydrogen gas occurs by transferring reducing equivalents produced by the fermentation of pyruvate to water. The natural cycle of hydrogen production and consumption by organisms is called the hydrogen cycle. Water splitting, the process by which water is broken down into its constituent protons, electrons, and oxygen, occurs in light reactions in all photosynthetic organisms. Some such organisms, including the algae Chlamydomonas Reinhardtii and cyanobacteria, have evolved a second stage in dark reactions in which protons and electrons are reduced to form H2 gas by specialized hydrogenases in the chloroplast. Attempts have been made to genetically modify cyanobacterial hydrases to efficiently synthesize H2 gas even in the presence of oxygen. Efforts have also been made using genetically modified algae in a bioreactor.
/mol (eV)
(according to Pauling)
substances
| H | 1 |
| 1,00794 | |
| 1s 1 | |
| Hydrogen | |
Hydrogen is the first element in the Periodic Table of the Elements. Widely distributed in nature. The cation (and nucleus) of the most common isotope of hydrogen 1 H is the proton. The properties of the 1 H nucleus make it possible to widely use NMR spectroscopy in the analysis of organic substances.
History of hydrogen
The release of combustible gas during the interaction of acids and metals was observed in the 16th and 17th centuries at the dawn of the formation of chemistry as a science. M. V. Lomonosov directly pointed to its isolation, but already definitely realizing that this was not phlogiston. The English physicist and chemist G. Cavendish in 1766 investigated this gas and called it "combustible air". When burned, "combustible air" produced water, but Cavendish's adherence to the theory of phlogiston prevented him from drawing the right conclusions. The French chemist A. Lavoisier, together with the engineer J. Meunier, using special gas meters, in 1783. carried out the synthesis of water, and then its analysis, decomposing water vapor with red-hot iron. Thus, he established that "combustible air" is part of the water and can be obtained from it.
Origin of the name hydrogen
Lavoisier named hydrogen hydrogène (from ὕδωρ - "water" and γενναω - "I give birth") - "giving birth to water." The Russian name "hydrogen" was proposed by the chemist M.F. Soloviev in 1824, by analogy with Lomonosov's "oxygen".
Hydrogen prevalence
In the Universe
Hydrogen is the most abundant element in the universe. It accounts for about 92% of all atoms (8% are helium atoms, the share of all other elements combined is less than 0.1%). Thus, hydrogen is the main component of stars and interstellar gas. Under conditions of stellar temperatures (for example, the surface temperature of the Sun is ~6000 °C), hydrogen exists in the form of plasma, in interstellar space this element exists in the form of individual molecules, atoms and ions and can form molecular clouds that differ significantly in size, density and temperature.
Earth's crust and living organisms
The mass fraction of hydrogen in the earth's crust is 1% - this is the tenth most common element. However, its role in nature is determined not by mass, but by the number of atoms, whose share among other elements is 17% (second place after oxygen, whose fraction of atoms is ~52%). Therefore, the importance of hydrogen in the chemical processes occurring on Earth is almost as great as that of oxygen. Unlike oxygen, which exists on Earth in both bound and free states, practically all hydrogen on Earth is in the form of compounds; only a very small amount of hydrogen in the form of a simple substance is found in the atmosphere (0.00005% by volume).
Hydrogen is a constituent of almost all organic substances and is present in all living cells. In living cells, by the number of atoms, hydrogen accounts for almost 50%.
Getting Hydrogen
Industrial methods for obtaining simple substances depend on the form in which the corresponding element is found in nature, that is, what can be the raw material for its production. So, oxygen, which is available in a free state, is obtained by a physical method - by isolation from liquid air. Almost all hydrogen is in the form of compounds, so chemical methods are used to obtain it. In particular, decomposition reactions can be used. One of the ways to produce hydrogen is the reaction of decomposition of water by electric current.
The main industrial method for producing hydrogen is the reaction with water of methane, which is part of natural gas. It is carried out at a high temperature (it is easy to verify that when methane is passed even through boiling water, no reaction occurs):
In the laboratory, to obtain simple substances, not necessarily natural raw materials are used, but those initial substances are chosen from which it is easier to isolate the necessary substance. For example, in the laboratory, oxygen is not obtained from the air. The same applies to the production of hydrogen. One of the laboratory methods for producing hydrogen, which is sometimes used in industry, is the decomposition of water by electric current.
Hydrogen is usually produced in the laboratory by reacting zinc with hydrochloric acid.
Getting hydrogen in industry
1. Electrolysis of aqueous solutions of salts:
2NaCl + 2H 2 O → H 2 + 2NaOH + Cl 2
2. Passing water vapor over hot coke at a temperature of about 1000°C:
H 2 O + ⇄ H 2 + CO
3.From natural gas.
Steam conversion:
CH 4 + H 2 O ⇄ CO + 3H 2 (1000 ° C)
Catalytic oxidation with oxygen:
2CH 4 + O 2 ⇄ 2CO + 4H 2
4. Cracking and reforming of hydrocarbons in the process of oil refining.
Obtaining hydrogen in the laboratory
1. Action of dilute acids on metals. To carry out such a reaction, zinc and dilute hydrochloric acid are most often used:
+2HCl → ZnCl 2 +H 2
2. Interaction of calcium with water: |
+ 2H 2 O → Ca (OH) 2 + H 2
3. Hydrolysis of hydrides:
NaH + H 2 O → NaOH + H 2
4. Action of alkalis on zinc or aluminum:
2 + 2NaOH + 6H 2 O → 2Na + 3H 2
+ 2KOH + 2H 2 O → K 2 + H 2
5.Using electrolysis. During the electrolysis of aqueous solutions of alkalis or acids, hydrogen is released at the cathode, for example:
2H 3 O + +2e - → H 2 +2H 2 O
Additional information about Hydrogen
Bioreactor for hydrogen production
Physical Properties of Hydrogen
Hydrogen emission spectrum
Emission spectrum of hydrogen
Hydrogen modifications can be separated by adsorption on active carbon at liquid nitrogen temperature. At very low temperatures, the equilibrium between orthohydrogen and parahydrogen is almost entirely shifted towards the latter. At 80 K, the aspect ratio is approximately 1:1. Desorbed parahydrogen is converted into orthohydrogen upon heating up to the formation of an equilibrium mixture at room temperature (ortho-para: 75:25). Without a catalyst, the transformation proceeds slowly (under conditions of the interstellar medium, with characteristic times up to cosmological times), which makes it possible to study the properties of individual modifications.
Hydrogen is the lightest gas, it is 14.5 times lighter than air. Obviously, the smaller the mass of molecules, the higher their speed at the same temperature. As the lightest, hydrogen molecules move faster than the molecules of any other gas and thus can transfer heat from one body to another faster. It follows that hydrogen has the highest thermal conductivity among gaseous substances. Its thermal conductivity is about seven times higher than that of air.
The hydrogen molecule is diatomic - H 2. Under normal conditions, it is a colorless, odorless and tasteless gas. Density 0.08987 g/l (n.o.), boiling point −252.76 °C, specific heat of combustion 120.9 10 6 J/kg, sparingly soluble in water — 18.8 ml/l. Hydrogen is highly soluble in many metals (, , etc.), especially in palladium (850 volumes per 1 volume of Pd). Related to the solubility of hydrogen in metals is its ability to diffuse through them; diffusion through a carbonaceous alloy (for example, steel) is sometimes accompanied by the destruction of the alloy due to the interaction of hydrogen with carbon (the so-called decarbonization). Practically insoluble in silver.
Phase diagram of hydrogen
Liquid hydrogen exists in a very narrow temperature range from −252.76 to −259.2 °C. It is a colorless liquid, very light (density at -253 °C 0.0708 g / cm 3) and fluid (viscosity at -253 °C 13.8 centigrade). The critical parameters of hydrogen are very low: temperature -240.2 °C and pressure 12.8 atm. This explains the difficulties in liquefying hydrogen. In the liquid state, equilibrium hydrogen consists of 99.79% para-H 2 , 0.21% ortho-H 2 .
Solid hydrogen, melting point −259.2 °C, density 0.0807 g/cm3 (at −262 °C) — snow-like mass, hexagonal crystals, space group P6/mmc, cell parameters a=3,75 c=6.12. At high pressure, hydrogen becomes metallic.
isotopes
Hydrogen occurs in the form of three isotopes, which have individual names: 1 H - protium (H), 2 H - deuterium (D), 3 H - tritium (radioactive) (T).
Protium and deuterium are stable isotopes with mass numbers 1 and 2. Their content in nature is 99.9885 ± 0.0070% and 0.0115 ± 0.0070%, respectively. This ratio may vary slightly depending on the source and method of hydrogen production.
The hydrogen isotope 3 H (tritium) is unstable. Its half-life is 12.32 years. Tritium is found in nature in very small amounts.
The literature also provides data on hydrogen isotopes with mass numbers 4–7 and half-lives 10–22–10–23 s.
Natural hydrogen consists of H 2 and HD (deuterohydrogen) molecules in a ratio of 3200:1. The content of pure deuterium hydrogen D 2 is even less. The concentration ratio of HD and D 2 is approximately 6400:1.
Of all the isotopes of chemical elements, the physical and chemical properties of hydrogen isotopes differ most from each other. This is due to the largest relative change in the masses of atoms.
| Temperature melting, K |
Temperature boiling, K |
Triple dot, K/kPa |
critical dot, K/kPa |
Density liquid/gas, kg/m³ |
|
|---|---|---|---|---|---|
| H2 | 13.95 | 20,39 | 13,96 /7,3 | 32,98 /1,31 | 70,811 /1,316 |
| HD | 16,60 | 22,13 | 16,60 /12,8 | 35,91 /1,48 | 114,80 /1,802 |
| HT | 22,92 | 17,63 /17,7 | 37,13 /1,57 | 158,62 /2,310 | |
| D2 | 18,62 | 23,67 | 18,73 /17,1 | 38,35 /1,67 | 162,50 /2,230 |
| DT | 24.38 | 19,71 /19,4 | 39,42 /1,77 | 211,54 /2,694 | |
| T2 | 25,04 | 20,62 /21,6 | 40,44 /1,85 | 260,17 /3,136 |
Deuterium and tritium also have ortho and para modifications: p-D2, o-D2, p-T2, o-T 2 . Heteroisotopic hydrogen (HD, HT, DT) do not have ortho and para modifications.
Chemical properties
Hydrogen molecules H 2 are quite strong, and in order for hydrogen to react, a lot of energy must be expended:
H 2 \u003d 2H - 432 kJ
Therefore, at ordinary temperatures, hydrogen reacts only with very active metals, such as calcium, forming calcium hydride:
H 2 \u003d CaH 2
and with the only non-metal - fluorine, forming hydrogen fluoride:
F 2 +H 2 \u003d 2HF
Hydrogen reacts with most metals and non-metals at elevated temperatures or under other influences, such as lighting:
O 2 + 2H 2 \u003d 2H 2 O
It can "take away" oxygen from some oxides, for example:
CuO + H 2 \u003d + H 2 O
The written equation reflects the reducing properties of hydrogen.
N 2 + 3H 2 → 2NH 3
Forms hydrogen halides with halogens:
F 2 + H 2 → 2HF, the reaction proceeds with an explosion in the dark and at any temperature, Cl 2 + H 2 → 2HCl, the reaction proceeds with an explosion, only in the light.
It interacts with soot at strong heating:
2H2→CH4
Interaction with alkali and alkaline earth metals
When interacting with active metals, hydrogen forms hydrides:
2 +H 2 → 2NaH +H 2 → CaH 2 +H 2 → MgH 2
hydrides- salt-like, solid substances, easily hydrolyzed:
CaH 2 + 2H 2 O → Ca (OH) 2 + 2H 2
Interaction with metal oxides (usually d-elements)
Oxides are reduced to metals:
CuO + H 2 → Cu + H 2 O Fe 2 O 3 + 3H 2 → 2Fe + 3H 2 O WO 3 + 3H 2 → W + 3H 2 O
Hydrogenation of organic compounds
Molecular hydrogen is widely used in organic synthesis for the reduction of organic compounds. These processes are called hydrogenation reactions. These reactions are carried out in the presence of a catalyst at elevated pressure and temperature. The catalyst can be either homogeneous (eg Wilkinson catalyst) or heterogeneous (eg Raney nickel, palladium on carbon).
Thus, in particular, during the catalytic hydrogenation of unsaturated compounds, such as alkenes and alkynes, saturated compounds, alkanes, are formed.
Geochemistry of hydrogen
Free hydrogen H 2 is relatively rare in terrestrial gases, but in the form of water it takes an exceptionally important part in geochemical processes.
Hydrogen can be present in minerals in the form of ammonium ion, hydroxyl ion, and crystalline water.
In the atmosphere, hydrogen is continuously produced as a result of the decomposition of water by solar radiation. Having a small mass, hydrogen molecules have a high rate of diffusion motion (it is close to the second cosmic velocity) and, getting into the upper layers of the atmosphere, can fly away into outer space.
Features of circulation
Application of hydrogen
Atomic hydrogen is used for atomic hydrogen welding.
Chemical industry
In the production of ammonia, methanol, soap and plastics
food industry
In the production of margarine from liquid vegetable oils.
Registered as a dietary supplement E949(packing gas)
Aviation industry
Hydrogen is very light and always rises in the air. Once upon a time, airships and balloons were filled with hydrogen. But in the 30s. XX century there were several accidents when the airships exploded and burned down. Nowadays airships are filled with helium.
Fuel
Hydrogen is used as rocket fuel. Research is underway on the use of hydrogen as a fuel for cars and trucks. Hydrogen engines do not pollute the environment and emit only water vapor.
Hydrogen-oxygen fuel cells use hydrogen to directly convert the energy of a chemical reaction into electrical energy.
Hydrogen, Hydrogenium, N (1)
As a combustible (flammable) air, hydrogen has been known for a long time. It was obtained by the action of acids on metals, the combustion and explosions of explosive gas were observed by Paracelsus, Boyle, Lemery and other scientists of the 16th-18th centuries. With the spread of the phlogiston theory, some chemists tried to make hydrogen as "free phlogiston". Lomonosov's dissertation "On metallic brilliance" describes the production of hydrogen by the action of "acid alcohols" (for example, "hydrochloric alcohol", i.e., hydrochloric acid) on iron and other metals; the Russian scientist was the first (1745) to put forward the hypothesis that hydrogen (“combustible vapor” - vapor inflammabilis) is a phlogiston. Cavendish, who studied in detail the properties of hydrogen, put forward a similar hypothesis in 1766. He called hydrogen "inflammable air" obtained from "metals" (Inflammable air from metals), and believed, like all phlogistics, that when dissolved in acids, the metal loses your phlogiston. Lavoisier, who in 1779 studied the composition of water through its synthesis and decomposition, called hydrogen Hydrogine (hydrogen), or Hydrogene (hydrogen), from Greek. gidor - water and gainome - I produce, give birth.
The nomenclature commission of 1787 adopted the word production Hydrogene from gennao, I give birth. In Lavoisier's Table of Simple Bodies, hydrogen (Hydrogene) is mentioned among the five (light, heat, oxygen, nitrogen, hydrogen) "simple bodies belonging to all three kingdoms of nature and which should be considered as elements of bodies"; as old synonyms for the name Hydrogene, Lavoisier calls combustible gas (Gaz inflammable), the base of combustible gas. In Russian chemical literature of the late 18th and early 19th centuries. there are two kinds of names for hydrogen: phlogistic (combustible gas, combustible air, flammable air, ignitable air) and antiphlogistic (water-creating, water-creating being, water-creating gas, hydrogen gas, hydrogen). Both groups of words are translations of the French names for hydrogen.
Hydrogen isotopes were discovered in the 1930s and quickly gained great importance in science and technology. At the end of 1931, Urey, Breckwedd and Murphy examined the residue after prolonged evaporation of liquid hydrogen and found in it heavy hydrogen with an atomic weight of 2. This isotope was called deuterium (Deuterium, D) from the Greek - another, second. Four years later, in water subjected to prolonged electrolysis, an even heavier isotope of hydrogen 3H was discovered, which was called tritium (Tritium, T), from Greek - the third.
