Boiling is the process of vaporization, which occurs when a liquid is brought to the boiling point. Every person knows from a school desk that water boils at t=100˚С. But many are interested in the question, which water boils faster: salty or fresh?

What is the boiling process

Boiling is a rather complex process consisting of four stages:

• First stage characterized by the appearance of small air bubbles that appear both on the surface of the liquid and on the side. Their occurrence is the result of the expansion of air bubbles located in microscopic cracks in the container.
• During the second stage you can see that the bubbles increase in volume and more and more of them are on top. This phenomenon is explained by an increase in temperature, at which the pressure on the bubbles increases. Thanks to the Archimedean force, they are on the surface. If it did not have time to warm up to the boiling point (100˚С), then the bubbles again go to the bottom, where the water is hotter. The noise characteristic of boiling is created by increasing and decreasing the size of the bubbles.
• At the third stage a mass of bubbles is observed, which, rising to the surface, causes a short-term turbidity of the water.
• Fourth stage characterized by intense seething and the appearance of large bubbles, which, bursting, create splashes. The latter say that the water has boiled over. Water vapor is produced, and the water makes the characteristic sounds of boiling.

Boiling fresh water

Boiling water is called water brought to a boil. During this process, an abundant formation of steam occurs, which is accompanied by the release of free oxygen molecules from the composition of the boiling liquid. Due to prolonged exposure to high temperatures, microbes and pathogenic bacteria die in boiling water. Therefore, if the quality of tap water is poor, it is undesirable to use it raw.

Fresh but hard water contains salts. During boiling, they form a coating on the walls of the kettle, which is often called scale. Boiling water is commonly used to make hot drinks or to disinfect fruits or vegetables.

When salt water boils

Experiments show that the boiling point of salt water is higher than the boiling point of fresh water. Therefore, we can conclude that fresh water boils faster. Salt water contains chloride and sodium ions, which are found among the water molecules. Between them, the process of hydration occurs - the addition of water molecules to salt ions.

It is worth noting that the hydration bond is much stronger than the water intermolecular bond. Therefore, during the boiling of fresh water, the process of vaporization begins faster. A liquid with salts dissolved in it requires a little more energy to boil, which in this situation is temperature.

When it rises, the molecules in salt water move much faster, but their number decreases, which means they collide less often. This can explain the smaller amount of steam - after all, its pressure is less than that of fresh water. In order to achieve pressure in salt water above atmospheric pressure and start boiling, a higher temperature is required.

Another justification

When cooking, many housewives salt the water at the beginning of the process, citing the fact that it boils faster this way. And some find an explanation for why salt water boils faster, based on school knowledge of a physics course, namely the topic of heat transfer. As you know, there are three types of heat transfer: heat transfer, which is characteristic of solids, convection, which is present in gaseous and liquid bodies, and radiation.

The latter type of heat transfer exists even in space. This is confirmed by the stars and, of course, the sun. But still, density is considered the main factor in this matter. Since salt water has a higher density than fresh water, it boils faster. However, it takes longer to freeze. Therefore, with a denser liquid, heat transfer will be more active, and boiling will occur faster.

Boiling Water Under Reduced Pressure: Video

Boiling is the process of changing the aggregate state of a substance. When we talk about water, we mean the change from liquid to vapor. It is important to note that boiling is not evaporation, which can occur even at room temperature. Also, do not confuse with boiling, which is the process of heating water to a certain temperature. Now that we have understood the concepts, we can determine at what temperature water boils.

Process

The very process of transforming the state of aggregation from liquid to gaseous is complex. And although people do not see it, there are 4 stages:

1. In the first stage, small bubbles form at the bottom of the heated container. They can also be seen on the sides or on the surface of the water. They are formed due to the expansion of air bubbles, which are always present in the cracks of the tank, where the water is heated.
2. In the second stage, the volume of the bubbles increases. All of them begin to rush to the surface, as there is saturated steam inside them, which is lighter than water. With an increase in the heating temperature, the pressure of the bubbles increases, and they are pushed to the surface due to the well-known Archimedes force. In this case, you can hear the characteristic sound of boiling, which is formed due to the constant expansion and reduction in the size of the bubbles.
3. In the third stage, a large number of bubbles can be seen on the surface. This initially creates cloudiness in the water. This process is popularly called "boiling with a white key", and it lasts a short period of time.
4. At the fourth stage, the water boils intensively, large bursting bubbles appear on the surface, and splashes may appear. Most often, splashes mean that the liquid has reached its maximum temperature. Steam will start to come out of the water.

It is known that water boils at a temperature of 100 degrees, which is possible only at the fourth stage.

Steam temperature

Steam is one of the states of water. When it enters the air, then, like other gases, it exerts a certain pressure on it. During vaporization, the temperature of steam and water remains constant until the entire liquid changes its state of aggregation. This phenomenon can be explained by the fact that during boiling all the energy is spent on converting water into steam.

At the very beginning of boiling, moist saturated steam is formed, which, after the evaporation of all the liquid, becomes dry. If its temperature begins to exceed the temperature of water, then such steam is superheated, and in terms of its characteristics it will be closer to gas.

Boiling salt water

It is interesting enough to know at what temperature water with a high salt content boils. It is known that it should be higher due to the content of Na+ and Cl- ions in the composition, which occupy an area between water molecules. This chemical composition of water with salt differs from the usual fresh liquid.

The fact is that in salt water a hydration reaction takes place - the process of attaching water molecules to salt ions. The bond between fresh water molecules is weaker than those formed during hydration, so boiling liquid with dissolved salt will take longer. As the temperature rises, the molecules in water containing salt move faster, but there are fewer of them, which is why collisions between them occur less frequently. As a result, less steam is produced and its pressure is therefore lower than the steam head of fresh water. Therefore, more energy (temperature) is required for full vaporization. On average, to boil one liter of water containing 60 grams of salt, it is necessary to raise the boiling point of water by 10% (that is, by 10 C).

Boiling pressure dependences

It is known that in the mountains, regardless of the chemical composition of water, the boiling point will be lower. This is because the atmospheric pressure is lower at altitude. Normal pressure is considered to be 101.325 kPa. With it, the boiling point of water is 100 degrees Celsius. But if you climb a mountain, where the pressure is on average 40 kPa, then the water will boil there at 75.88 C. But this does not mean that cooking in the mountains will take almost half the time. For heat treatment of products, a certain temperature is needed.

It is believed that at an altitude of 500 meters above sea level, water will boil at 98.3 C, and at an altitude of 3000 meters, the boiling point will be 90 C.

Note that this law also works in the opposite direction. If a liquid is placed in a closed flask through which vapor cannot pass, then as the temperature rises and steam is formed, the pressure in this flask will increase, and boiling at elevated pressure will occur at a higher temperature. For example, at a pressure of 490.3 kPa, the boiling point of water will be 151 C.

Boiling distilled water

Distilled water is purified water without any impurities. It is often used for medical or technical purposes. Given that there are no impurities in such water, it is not used for cooking. It is interesting to note that distilled water boils faster than ordinary fresh water, but the boiling point remains the same - 100 degrees. However, the difference in boiling time will be minimal - only a fraction of a second.

in a teapot

Often people are interested in what temperature water boils in a kettle, since it is these devices that they use to boil liquids. Taking into account the fact that the atmospheric pressure in the apartment is equal to the standard one, and the water used does not contain salts and other impurities that should not be there, then the boiling point will also be standard - 100 degrees. But if the water contains salt, then the boiling point, as we already know, will be higher.

Conclusion

Now you know at what temperature water boils, and how atmospheric pressure and the composition of the liquid affect this process. There is nothing complicated in this, and children receive such information at school. The main thing to remember is that with a decrease in pressure, the boiling point of the liquid also decreases, and with its increase, it also increases.

On the Internet, you can find many different tables that indicate the dependence of the boiling point of a liquid on atmospheric pressure. They are available to everyone and are actively used by schoolchildren, students and even teachers in institutes.

I wrote in Russian that boiling water lie down

No, it's not Russian.

Quote: Vladimir S

Just do not eat all the boiling water in surprise.

A very simple and memorable advice on how to stop confusing these verbs that are similar in meaning forever.

So, the verb "lay down" without a prefix is ​​not used. Therefore, if you desperately need to use it, then feel free to add any prefix that is suitable in meaning and go ahead: put, lay out, lay, shift, fold, etc.

But the verb "put", on the contrary, for some reason does not like prefixes. But on the other hand, he loves when the accent is correctly placed in it: put, put, put (wrong - put), participle put, put participle.

only a chemist can benefit from Google Chemistry

It depends on the individual. You can look into a book and see a fig.

The scale in the kettle is salt, albeit sparingly soluble, i.e. theoretically, water in a kettle with scale will boil at t greater than 100

And you got that the sea is salty, because salted herrings swim in it

Theoretically, in terms of b.b. and b.m. magnitudes, salted herrings thrown into the fresh sea can make it salty. Again, it is necessary to see how many herrings will be.

Without increasing the pressure above one hundred degrees, even Einstein will not heat up.

He won't be able to do this in a laboratory, but an ordinary citizen, in an ordinary kitchen, in an ordinary microwave oven - easily.
And further

And in general, the North was not interested in some kind of boiling centers, but why bonds in hydrated ions

That's exactly what he's not interested in.

Quote: North

If you add salt to the water, it will boil faster.

As we have repeatedly seen above, water without salt can easily be overheated, but it will take more time. If it is salted in advance, then it will take less time, the water will not be overheated, it will boil at 100 ° C.

And despite the fact that water begins to boil at a higher temperature with increasing salt concentration, it theoretically turns out that if you add salt, it will boil earlier. But the examples show that not only theoretically, but also quite practically. And why he said theoretically - because it is still desirable, or even necessary, to take purified water, or even distilled, and the dishes should be clean, smooth.

In an ordinary kitchen, this is not always the case. Usually we boil water as it is, often even from the tap, in ordinary scratched dishes, and salt not for tea, but for soup, that is, other ingredients are present along with salt. There can be no talk of any overheating here. But the questioner didn't provide details.

Boilers are neutral, they do not affect the boiling point.

boiling water falls into the water even before the start of heating

Boilers are a developed rough, spongy, porous surface. We will consider in this capacity the roughness of the surface of the glass bulb.

1. Flask with fresh bidistillate. Everywhere is clean.
2. A flask with a roughness invisible to the eye.
3. A flask with a bottom scratched on the inside with sandpaper.

In all three, the boiling point will be different. boiling, that's what he was talking about. North. Although the temperature boiling in all three cases, of course, will be the same.

By the way, food should be salted after it is ready. I nearly not salt. Not after reading Bragg, but since childhood, such are taste preferences.

Why is it easier to swim in salt water than in fresh water?

It is easier to swim in salt water than in fresh water, because salt makes the water heavier: if you take two cylinders of the same capacity, one of which is salt water and the other fresh water, then the salt water cylinder will weigh a little more. And the greater the density (weight) of water, the easier it is to swim in it.

An object can float in a liquid if its weight is equal to the weight of the water it displaces or pushes out (water is displaced in order to make room for the object). You can look at it from the other side: when you sit in the bath, you see that the water level in it rises. If you knock off the water that your body has displaced, the weight of that water will be equal to the weight of your body. If the water has a higher density, like salt water, then your body will displace less of it (i.e., it will take less water to equalize with your body weight), and you will be higher when you float up than if you floated in fresh water.

In the first glass is ordinary fresh water, in the second - salty,
in the third - very salty.

What retains heat better: fresh water or salt water?

Two vessels were filled with fresh water. They were warmed up for about 10 minutes. Then 2 tablespoons of salt were added to one of the vessels and labeled "salt water". At the first attempt, there was not much difference, the temperature was 120 degrees. At the second attempt, another 2 tablespoons of salt were added and the difference became noticeable. Salt water cooled much faster than ordinary tap water. As part of the experiment, the amount of salt in the water was monitored. When the water temperature reached 90 degrees, data collection began. The same thermometers were used throughout the experiment.

Why is ocean water salty?

Salt from the surface of the Earth is constantly dissolved and ends up in the ocean.
If all the oceans were dried up, the remaining salt could be used to build a wall 230 km high and almost 2 km thick. Such a wall could circle the entire globe along the equator. Or another comparison. The salt of all the dried up oceans is 15 times the volume of the entire European continent!
Ordinary salt is obtained from sea water, salt sources or from the development of rock salt deposits. Sea water contains 3-3.5% salt. Inland seas, such as the Mediterranean Sea, the Red Sea, contain more salt than the open seas. The Dead Sea, occupying only 728 sq. km., contains approximately 10,523,000,000 tons of salt.
On average, a liter of sea water contains about 30 g of salt. Deposits of rock salt in various parts of the earth were formed many millions of years ago as a result of the evaporation of sea water. For the formation of rock salt, nine-tenths of the volume of sea water must be evaporated; it is believed that inland seas were located on the site of modern deposits of this salt. They evaporated faster than the new sea water came in - that's where the deposits of rock salt appeared.
The main amount of edible salt is extracted from rock salt. Usually mines are laid to salt deposits. Clean water is pumped through the pipes, which dissolves the salt. Through the second pipe, this solution rises to the surface.

Why does fresh water boil faster than salt water?

Salt water boils at a higher temperature than fresh water, respectively, under the same heating conditions, fresh water will boil faster, salty water will boil later. There is a whole physico-chemical theory why this is the case, "on the fingers" it can be explained as follows. Water molecules bind to salt ions - the process of hydration occurs. The bond between water molecules is weaker than the bond formed as a result of hydration. Therefore, a fresh water molecule is more easily (at a lower temperature) detached from its "environment" - i.e. literally evaporates. And in order for a water molecule with a dissolved salt to “break out of the embrace” of salt and other water molecules, more energy is required, i.e. high temperature.

To cook food faster, most housewives add salt to the pan before the water starts to boil. In their opinion, this will speed up the cooking process. Others, on the contrary, argue that tap water boils much faster. To answer this question, you need to turn to the laws of physics and chemistry. Why does salt water boil faster than regular water, and is it really so? Let's find out! Details in the article below.

Why salt water boils faster: physical laws of boiling

In order to understand what processes begin to occur when a liquid is heated, it is necessary to know what scientists mean by the technology of the boiling process.

Any water, ordinary or salty, starts to boil in exactly the same way. This process goes through several stages:

• small bubbles begin to form on the surface;
• an increase in the size of the bubbles;
• their settling to the bottom;
• the liquid becomes cloudy;
• boiling process.

Why does salt water boil faster?

Supporters of salted water say that when heated, the heat transfer theory works. However, the heat released after the destruction of the molecular lattice does not have much effect. Much more important is the technological process of hydration. At this time, strong molecular bonds are formed. So why does salt water boil faster?

When they become very strong, it is much more difficult for air bubbles to move. It takes a long time to move up or down. In other words, if there is salt in the water, the air circulation process slows down. As a result, salt water boils a little slower. Air bubbles are prevented from moving by molecular bonds. That's why it doesn't boil faster than unsalted.

Can you do without salt?

The debate about how fast salt or tap water boils can go on forever. If you look at the practical application, there will not be much difference. This is easily explained by the laws of physics. Water begins to boil when the temperature reaches 100 degrees. This value may change if the air density parameters change. For example, water high in the mountains begins to boil at temperatures below 100 degrees. In domestic conditions, the most important indicator is the power of the gas burner, as well as the heating temperature of the electric stove. The speed of heating the liquid, as well as the time required for boiling, depend on these parameters.

At the fire, the water begins to boil after a few minutes, since the burned firewood emits much more heat than a gas stove, and the area of ​​\u200b\u200bthe heated surface is much larger. From this we can draw a simple conclusion: in order to achieve a quick boil, you need to turn on the gas burner at maximum power, and not add salt.

Any water starts to boil at the same temperature (100 degrees). But the speed of boiling can be different. Salt water will start to boil later because of the air bubbles, which are much more difficult to break molecular bonds. I must say that distilled water boils faster than ordinary tap water. The fact is that in purified, distilled water there are no strong molecular bonds, there are no impurities, so it starts to heat up much faster.

Conclusion

The boiling time of ordinary or salt water differs by several seconds. It has no effect on the speed of cooking. Therefore, you should not try to save time on boiling, it is better to start strictly observing the laws of cooking. To make the dish tasty, it needs to be salted at a certain time. That's why salt water doesn't always boil faster!