Lecture 1 Chemical thermodynamics. Chemical kinetics and catalysis PLAN 1. Basic concepts of thermodynamics. 2. Thermochemistry. 3. Chemical equilibrium. 4. Rate of chemical reactions. 5. The influence of temperature on the rate of reactions. 6. The phenomenon of catalysis. Prepared by: Ph.D., Associate Professor. Ivanets L.M., as. Kozachok S.S. Lecturer assistant of the department of pharmaceutical chemistry Kozachok Solomeya Stepanovna
Thermodynamics - Thermodynamics is a branch of physics that studies the mutual transformations of various types of energy associated with the transition of energy in the form of heat and work. The great practical importance of thermodynamics is that it allows one to calculate the thermal effects of a reaction, to indicate in advance the possibility or impossibility of carrying out a reaction, as well as the conditions for its occurrence.
Internal energy Internal energy is the kinetic energy of all particles of the system (molecules, atoms, electrons) and the potential energy of their interactions, in addition to the kinetic and potential energy of the system as a whole. Internal energy is a function of state, i.e. its change is determined by the given initial and final states of the system and does not depend on the process path: U = U 2 – U 1
The first law of thermodynamics Energy does not disappear without a trace and does not arise from nothing, but only passes from one type to another in equivalent quantities. A perpetual motion machine of the first kind, that is, a periodically operating machine that produces work without wasting energy, is impossible. Q = U + W In any isolated system, the total energy supply remains unchanged. Q = U + W
The thermal effect of a chemical reaction at constant V or p does not depend on the reaction path, but is determined by the nature and state of the starting materials and reaction products. Hess's Law H 1 H 2 H 3 H 4 Starting substances, reaction products H 1 = H 2 + H 3 + H 4 H 1 = H 2 + H 3 + H 4
The second law of thermodynamics, like the first, is the result of centuries of human experience. There are different formulations of the second law, but they all determine the direction of spontaneous processes: 1. Heat cannot spontaneously transfer from a cold body to a hot one (Clausius’s postulate). 2. A process whose only result is the conversion of heat into work is impossible (Thomson's postulate). 3. It is impossible to build a periodic machine that only cools the thermal reservoir and does work (Planck’s first postulate). 4. Any form of energy can be completely converted into heat, but heat is only partially converted into other types of energy (Planck’s second postulate).
Entropy is a thermodynamic function of state, therefore its change does not depend on the path of the process, but is determined only by the initial and final states of the system. then S 2 - S 1 = ΔS = S 2 - S 1 = ΔS = The physical meaning of entropy is the amount of bound energy, which is related to one degree: in isolated systems, the direction of the flow of spontaneous processes is determined by the change in entropy.
Characteristic functions U – function of the isochoric-isentropic process: dU = TdS – pdV. For an arbitrary process: U 0 Н – function of an isobaric-isentropic process: dН = TdS + Vdp For an arbitrary process: Н 0 S – function of an isolated system For an arbitrary process: S 0 For an arbitrary process: S 0 F – function of an isochoric-isothermal process dF = dU – TdS. For an arbitrary process: F 0 G – function of an isobaric-isothermal process: dG = dH- TdS For an arbitrary process: G 0
Classification of chemical reactions according to the number of stages Simple ones proceed in one elementary chemical act Complex ones proceed in several stages Reverse reaction A B Reverse reaction: A B Parallel: B A C Sequential: ABC Conjugate: A D Conjugate: A D C B E B E
The influence of temperature on the rate of reactions The influence of temperature on the rate of enzymatic reactions t t
Van't Hoff comparison: Calculation of the shelf life of drugs using the Van't Hoff "accelerated aging" method: at t 2 t 1 Temperature rate coefficient:
Solving problems for the section
The topic “Chemical thermodynamics and kinetics,” which involves the study of conditions affecting the rate of a chemical reaction, appears twice in the school chemistry course – in the 9th and 11th grades. However, this particular topic is one of the most difficult and quite complex not only for understanding by the “average” student, but even for presentation by some teachers, especially non-specialists working in rural areas, for whom chemistry is an additional subject, taking into account the hours of which the teacher accumulates rate, and therefore hope for a more or less decent salary.
In conditions of a sharp decrease in the number of students in rural schools, due to well-known reasons, the teacher is forced to be a generalist. After attending 2-3 courses, he begins teaching subjects that are often very far from his main specialty.
This development is aimed primarily at beginning teachers and subject specialists who are forced to teach chemistry in a market economy. The material contains tasks on finding the rates of heterogeneous and homogeneous reactions and increasing the reaction rate with increasing temperature. Despite the fact that these problems are based on school material, although difficult for the “average” student to master, it is advisable to solve several of them in a chemistry lesson in
11th grade, and offer the rest at a club or elective lesson to students who plan to connect their future destiny with chemistry.
In addition to problems analyzed in detail and provided with answers, this development contains theoretical material that will help a chemistry teacher, primarily a non-specialist, understand the essence of this complex topic in a general chemistry course.
Based on the proposed material, you can create your own version of a lesson-lecture, depending on the abilities of the students in the class, and you can use the proposed theoretical part when studying this topic in both the 9th and 11th grades.
Finally, the material contained in this development will be useful for a graduate preparing to enter a university, including one in which chemistry is a major subject, to analyze independently.
Theoretical part on the topic
"Chemical thermodynamics and kinetics"
Conditions affecting the rate of a chemical reaction
1. The rate of a chemical reaction depends on the nature of the reacting substances.
EXAMPLES.
Metallic sodium, which is alkaline in nature, reacts violently with water, releasing a large amount of heat, in contrast to zinc, which is amphoteric in nature, which reacts with water slowly and when heated:
Powdered iron reacts more vigorously with strong mineral hydrochloric acid than with weak organic acetic acid:
2. The rate of a chemical reaction depends on the concentration of the reactants, whether in a dissolved or gaseous state.
EXAMPLES.
In pure oxygen, sulfur burns more energetically than in air:
Powdered magnesium reacts more vigorously with a 30% solution of hydrochloric acid than with a 1% solution:
3. The rate of a chemical reaction is directly proportional to the surface area of the reacting substances in the solid state of aggregation.
EXAMPLES.
A piece of charcoal (carbon) is very difficult to light with a match, but charcoal dust burns explosively:
C + O 2 = CO 2.
Aluminum in the form of granules does not react quantitatively with the iodine crystal, but crushed iodine combines vigorously with aluminum in the form of powder:
4. The rate of a chemical reaction depends on the temperature at which the process occurs.
EXAMPLE
For every 10 °C increase in temperature, the rate of most chemical reactions increases by 2–4 times. A specific increase in the rate of a chemical reaction is determined by a specific temperature coefficient (gamma).
Let's calculate how many times the reaction rate will increase:
2NO + O 2 = 2NO 2,
if the temperature coefficient is 3 and the process temperature has increased from 10 °C to 50 °C.
The temperature change is:
t= 50 °C – 10 °C = 40 °C.
We use the formula:
where is the rate of a chemical reaction at elevated temperature, is the rate of a chemical reaction at the initial temperature.
Consequently, the rate of a chemical reaction when the temperature increases from 10 °C to 50 °C will increase by 81 times.
5. The rate of a chemical reaction depends on the presence of certain substances.
Catalyst is a substance that accelerates the course of a chemical reaction, but is not consumed during the reaction. A catalyst lowers the activation barrier of a chemical reaction.
Inhibitor is a substance that slows down the progress of a chemical reaction, but is not consumed during the reaction process.
EXAMPLES.
The catalyst that accelerates this chemical reaction is manganese(IV) oxide.
The catalyst that accelerates this chemical reaction is red phosphorus.
An inhibitor that slows down the progress of this chemical reaction is an organic substance - methenamine (hexamethylenetetramine).
The rate of a homogeneous chemical reaction is measured by the number of moles of the substance that reacted or formed as a result of the reaction per unit time per unit volume:
where homog is the rate of a chemical reaction in a homogeneous system, is the number of moles of one of the substances that entered into the reaction or one of the substances formed as a result of the reaction, V- volume,
t– time, – change in the number of moles of a substance during the reaction t.
Since the ratio of the number of moles of a substance to the volume of the system represents the concentration With, That
Hence:
The rate of a homogeneous chemical reaction is measured in mol/(l s).
Taking this into account, the following definition can be given:
the rate of a homogeneous chemical reaction is equal to the change in the concentration of one of the substances that entered into the reaction or one of the substances formed as a result of the reaction per unit time.
If a reaction occurs between substances in a heterogeneous system, then the reacting substances do not come into contact with each other throughout the entire volume, but only on the surface of the solid. For example, when a piece of crystalline sulfur burns, oxygen molecules react only with those sulfur atoms that are on the surface of the piece. When a piece of sulfur is crushed, the reacting surface area increases and the rate of sulfur combustion increases.
In this regard, the definition of the rate of a heterogeneous chemical reaction is as follows:
the rate of a heterogeneous chemical reaction is measured by the number of moles of the substance that reacted or formed as a result of the reaction per unit time on a unit surface:
Where S– surface area.
The rate of a heterogeneous chemical reaction is measured in mol/(cm 2 s).
Tasks on the topic
"Chemical thermodynamics and kinetics"
1. 4 moles of nitrogen(II) oxide and excess oxygen were introduced into the vessel for chemical reactions. After 10 s, the amount of nitrogen oxide(II) substance turned out to be 1.5 mol. Find the rate of this chemical reaction if it is known that the volume of the vessel is 50 liters.
2. The amount of methane substance in the vessel for carrying out chemical reactions is 7 mol. Excess oxygen was introduced into the vessel and the mixture was exploded. It was experimentally established that after 5 s the amount of methane substance decreased by 2 times. Find the rate of this chemical reaction if it is known that the volume of the vessel is 20 liters.
3. The initial concentration of hydrogen sulfide in the gas combustion vessel was 3.5 mol/l. Excess oxygen was introduced into the vessel and the mixture was exploded. After 15 s, the hydrogen sulfide concentration was 1.5 mol/l. Find the rate of this chemical reaction.
4. The initial concentration of ethane in the gas combustion vessel was 5 mol/L. Excess oxygen was introduced into the vessel and the mixture was exploded. After 12 s, the ethane concentration was 1.4 mol/L. Find the rate of this chemical reaction.
5. The initial concentration of ammonia in the gas combustion vessel was 4 mol/l. Excess oxygen was introduced into the vessel and the mixture was exploded. After 3 s, the ammonia concentration was 1 mol/l. Find the rate of this chemical reaction.
6. The initial concentration of carbon monoxide (II) in the gas combustion vessel was 6 mol/l. Excess oxygen was introduced into the vessel and the mixture was exploded. After 5 s, the concentration of carbon(II) monoxide was halved. Find the rate of this chemical reaction.
7. A piece of sulfur with a reacting surface area of 7 cm2 was burned in oxygen to form sulfur(IV) oxide. In 10 s, the amount of sulfur substance decreased from 3 mol to 1 mol. Find the rate of this chemical reaction.
8. A piece of carbon with a reacting surface area of 10 cm 2 was burned in oxygen to form carbon monoxide (IV). In 15 s, the amount of carbon substance decreased from 5 mol to 1.5 mol. Find the rate of this chemical reaction.
9.
A cube of magnesium with a total reacting surface area of 15 cm 2 and the amount of substance
6 moles burned in excess oxygen. Moreover, 7 s after the start of the reaction, the amount of magnesium substance turned out to be equal to 2 mol. Find the rate of this chemical reaction.
10. A calcium bar with a total reacting surface area of 12 cm 2 and an amount of substance of 7 mol was burned in excess oxygen. Moreover, 10 s after the start of the reaction, the amount of calcium substance turned out to be 2 times less. Find the rate of this chemical reaction.
Solutions and Answers
1 (NO) = 4 mol,
O 2 – excess,
t 2 = 10 s,
t 1 = 0 s,
2 (NO) = 1.5 mol,
Find:
Solution
2NO + O 2 = 2NO 2.
Using the formula:
R-tions = (4 – 1.5)/(50 (10 – 0)) = 0.005 mol/(l s).
Answer. r-tion = 0.005 mol/(l s).
2.
1 (CH 4) = 7 mol,
O 2 – excess,
t 2 = 5 s,
t 1 = 0 s,
2 (CH 4) = 3.5 mol,
Find:
Solution
CH 4 + 2O 2 = CO 2 + 2H 2 O.
Using the formula:
Let's find the rate of this chemical reaction:
R-tions = (7 – 3.5)/(20 (5 – 0)) = 0.035 mol/(l s).
Answer. r-tion = 0.035 mol/(l s).
3.
s 1 (H 2 S) = 3.5 mol/l,
O 2 – excess,
t 2 = 15 s,
t 1 = 0 s,
With 2 (H 2 S) = 1.5 mol/l.
Find:
Solution
2H 2 S + 3O 2 = 2SO 2 + 2H 2 O.
Using the formula:
Let's find the rate of this chemical reaction:
R-tions = (3.5 – 1.5)/(15 – 0) = 0.133 mol/(l s).
Answer. r-tion = 0.133 mol/(l s).
4.
c 1 (C 2 H 6) = 5 mol/l,
O 2 – excess,
t 2 = 12 s,
t 1 = 0 s,
c 2 (C 2 H 6) = 1.4 mol/l.
Find:
Solution
2C 2 H 6 + 7O 2 = 4CO 2 + 6H 2 O.
Let's find the rate of this chemical reaction:
R-tions = (6 – 2)/(15 (7 – 0)) = 0.0381 mol/(cm 2 s).
Answer. r-tion = 0.0381 mol/(cm 2 s).
10. Answer. r-tion = 0.0292 mol/(cm 2 s).
Literature
Glinka N.L. General Chemistry, 27th ed. Ed. V.A. Rabinovich. L.: Chemistry, 1988; Akhmetov N.S. General and inorganic chemistry. M.: Higher. school, 1981; Zaitsev O.S. General chemistry. M.: Higher. shk, 1983; Karapetyants M.Kh., Drakin S.I. General and inorganic chemistry. M.: Higher. school, 1981; Korolkov D.V. Fundamentals of inorganic chemistry. M.: Education, 1982; Nekrasov B.V. Fundamentals of general chemistry. 3rd ed., M.: Khimiya, 1973; Novikov G.I. Introduction to inorganic chemistry. Part 1, 2. Minsk: Higher. school, 1973–1974; Shchukarev S.A.. Inorganic chemistry. T. 1, 2. M.: Vyssh. school, 1970–1974; Schröter W., Lautenschläger K.-H., Bibrak H. et al. Chemistry. Reference ed. Per. with him. M.: Khimiya, 1989; Feldman F.G., Rudzitis G.E. Chemistry-9. Textbook for 9th grade of secondary school. M.: Education, 1990; Feldman F.G., Rudzitis G.E. Chemistry-9. Textbook for 9th grade of secondary school. M.: Education, 1992.
“FUNDAMENTALS OF CHEMICAL THERMODYNAMICS, CHEMICAL KINETICS AND EQUILIBRIUM”
Fundamentals of chemical thermodynamics
1 . What does chemical thermodynamics study:
1) the rate of chemical transformations and the mechanisms of these transformations;
2) energy characteristics of physical and chemical processes and the ability of chemical systems to perform useful work;
3) conditions for shifting chemical equilibrium;
4) the influence of catalysts on the rate of biochemical processes.
2. An open system is a system that:
3. A closed system is a system that:
1) does not exchange either matter or energy with the environment;
2) exchanges both matter and energy with the environment;
3) exchanges energy with the environment, but does not exchange matter;
4) exchanges matter with the environment, but does not exchange energy.
4. An isolated system is a system that:
1) does not exchange either matter or energy with the environment;
2) exchanges both matter and energy with the environment;
3) exchanges energy with the environment, but does not exchange matter;
4) exchanges matter with the environment, but does not exchange energy.
5. To what type of thermodynamic systems does the solution located in a sealed ampoule placed in a thermostat belong?
1) isolated;
2) open;
3) closed;
4) stationary.
6. What type of thermodynamic systems does the solution in the sealed ampoule belong to?
1) isolated;
2) open;
3) closed;
4) stationary.
7. What type of thermodynamic systems does a living cell belong to?
1) open;
2) closed;
3) isolated;
4) equilibrium.
8 . What parameters of a thermodynamic system are called extensive?
1) the magnitude of which does not depend on the number of particles in the system;
3) the value of which depends on the state of aggregation of the system;
9. What parameters of a thermodynamic system are called intensive?
!) whose magnitude does not depend on the number of particles in the system;
2) the magnitude of which depends on the number of particles in the system;
3) the value of which depends on the state of aggregation;
4) the magnitude of which depends on time.
10 . Functions of the state of a thermodynamic system are quantities that:
1) depend only on the initial and final state of the system;
2) depend on the process path;
3) depend only on the initial state of the system;
4) depend only on the final state of the system.
11 . What quantities are functions of the state of the system: a) internal energy; b) work; c) warmth; d) enthalpy; d) entropy.
3) all quantities;
4) a, b, c, d.
12 . Which of the following properties are intensive: a) density; b) pressure; c) mass; d) temperature; e) enthalpy; e) volume?
3) b, c, d, f;
13. Which of the following properties are extensive: a) density; b) pressure; c) mass; d) temperature; e) enthalpy; e) volume?
3) b, c, d, f;
14 . What forms of energy exchange between the system and the environment are considered by thermodynamics: a) heat; b) work; c) chemical; d) electric; e) mechanical; e) nuclear and solar?
2) c, d, e, f;
3) a, c, d, e, f;
4) a, c, d, e.
15. Processes occurring at a constant temperature are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
16 . Processes occurring at constant volume are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
17 . Processes occurring at constant pressure are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
18 . The internal energy of a system is: 1) the entire energy reserve of the system, except for the potential energy of its position and the kinetic energy of the system as a whole;
2) the entire energy reserve of the system;
3) the entire energy reserve of the system, except for the potential energy of its position;
4) a quantity characterizing the degree of disorder in the arrangement of particles of the system.
19 . What law reflects the relationship between work, heat and internal energy of a system?
1) the second law of thermodynamics;
2) Hess's law;
3) the first law of thermodynamics;
4) van't Hoff's law.
20 . The first law of thermodynamics reflects the relationship between:
1) work, heat and internal energy;
2) Gibbs free energy, enthalpy and entropy of the system;
3) work and heat of the system;
4) work and internal energy.
21 . Which equation is the mathematical expression of the first law of thermodynamics for isolated systems?
l)AU=0 2)AU=Q-p-AV 3)AG = AH-TAS
22 . Which equation is the mathematical expression of the first law of thermodynamics for closed systems?
1)AU=0; 2)AU=Q-p-AV;
3) AG = AH - T*AS;
23 . Is the internal energy of an isolated system a constant or variable quantity?
1) constant;
2) variable.
24 . In an isolated system, the reaction of hydrogen combustion occurs with the formation of liquid water. Does the internal energy and enthalpy of the system change?
1) internal energy will not change, enthalpy will change;
2) internal energy will change, enthalpy will not change;
3) internal energy will not change, enthalpy will not change;
4) internal energy will change, enthalpy will change.
25 . Under what conditions is the change in internal energy equal to the heat received by the system from the environment?
1) at constant volume;
3) at constant pressure;
4) under no circumstances.
26 . The thermal effect of a reaction occurring at constant volume is called a change:
1) enthalpy;
2) internal energy;
3) entropy;
4) Gibbs free energy.
27 . The enthalpy of a reaction is:
28. Chemical processes during which the enthalpy of the system decreases and heat is released into the external environment are called:
1) endothermic;
2) exothermic;
3) exergonic;
4) endergonic.
29 . Under what conditions is the change in enthalpy equal to the heat received by the system from the environment?
1) at constant volume;
2) at constant temperature;
3) at constant pressure;
4) under no circumstances.
30 . The thermal effect of a reaction occurring at constant pressure is called a change:
1) internal energy;
2) none of the previous definitions are correct;
3) enthalpy;
4) entropy.
31. What processes are called endothermic?
32 . What processes are called exothermic?
1) for which AN is negative;
2) for which AG is negative;
3) for which AN is positive;
4) for which AG is positive.
33 . Specify the formulation of Hess's law:
1) the thermal effect of the reaction depends only on the initial and final state of the system and does not depend on the reaction path;
2) the heat absorbed by the system at a constant volume is equal to the change in the internal energy of the system;
3) the heat absorbed by the system at constant pressure is equal to the change in enthalpy of the system;
4) the thermal effect of the reaction does not depend on the initial and final state of the system, but depends on the reaction path.
34. What law underlies the calculation of caloric content of food?
1) van't Hoff;
3) Sechenov;
35. When oxidizing which substances under body conditions, more energy is released?
1) proteins;
3) carbohydrates;
4) carbohydrates and proteins.
36 . A spontaneous process is a process that:
1) carried out without the help of a catalyst;
2) accompanied by the release of heat;
3) carried out without external energy consumption;
4) proceeds quickly.
37 . Entropy of a reaction is:
1) the amount of heat that is released or absorbed during a chemical reaction under isobaric-isothermal conditions;
2) the amount of heat that is released or absorbed during a chemical reaction under isochoric-isothermal conditions;
3) a value characterizing the possibility of spontaneous occurrence of the process;
4) a quantity characterizing the degree of disorder in the arrangement and movement of particles in the system.
38 . What state function characterizes the tendency of a system to achieve a probable state that corresponds to the maximum randomness of the distribution of particles?
1) enthalpy;
2) entropy;
3) Gibbs energy;
4) internal energy.
39 . What is the relationship between the entropies of three aggregate states of one substance: gas, liquid, solid:
I) S (g) > S (g) > S (tv); 2) S(solid)>S(g)>S(g); 3)S(g)>S(g)>S(TB); 4) the state of aggregation does not affect the entropy value.
40 . Which of the following processes should exhibit the greatest positive change in entropy:
1) CH3OH (s) --> CH,OH (g);
2) CH4OH (s) --> CH 3 OH (l);
3) CH,OH (g) -> CH4OH (s);
4) CH,OH (l) -> CH3OH (sol).
41 . Choose the correct statement: the entropy of the system increases when:
1) increased pressure;
2) transition from liquid to solid state of aggregation
3) increase in temperature;
4) transition from gaseous to liquid state.
42. What thermodynamic function can be used to predict whether a reaction will occur spontaneously in an isolated system?
1) enthalpy;
2) internal energy;
3) entropy;
4) potential energy of the system.
43 . Which equation is the mathematical expression of the 2nd law of thermodynamics for isolated systems?
44 . If the system reversibly receives a quantity of heat Q at temperature T, then about T;
2) increases by the amount Q/T;
3) increases by an amount greater than Q/T;
4) increases by an amount less than Q/T.
45 . In an isolated system, a chemical reaction occurs spontaneously to form a certain amount of product. How does the entropy of such a system change?
1) increases
2) decreases
3) does not change
4) reaches the minimum value
46 . Indicate in which processes and under what conditions the change in entropy can be equal to the work of the process?
1) in isobaric conditions, at constant P and T;
2) in isochoric conditions, at constant V and T;
H) the change in entropy is never equal to work; 4) in isothermal conditions, at constant P and 47 . How will the bound energy of the system TS change when heated and when it condenses?
1) increases with heating, decreases with condensation;
2) decreases with heating, increases with condensation;
3) there is no change in T-S;
4) increases with heating and condensation.
48 . What parameters of the system must be kept constant so that the sign of the change in entropy can be used to judge the direction of the spontaneous course of the process?
1) pressure and temperature;
2) volume and temperature;
3) internal energy and volume;
4) only temperature.
49 . In an isolated system, all spontaneous processes proceed in the direction of increasing disorder. How does entropy change?
1) does not change;
2) increases;
3) decreases;
4) first increases and then decreases.
50 . Entropy increases by the amount Q/T for:
1) reversible process;
2) irreversible process;
3) homogeneous;
4) heterogeneous.
51 How does the entropy of the system change due to forward and reverse reactions during ammonia synthesis?
3) entropy does not change during the reaction;
4) entropy increases for forward and reverse reactions.
52 . What simultaneously acting factors determine the direction of a chemical process?
1) enthalpy and temperature;
2) enthalpy and entropy;
3) entropy and temperature;
4) changes in Gibbs energy and temperature.
53. Under isobaric-isothermal conditions, the maximum work performed by the system is:
1) equal to the decrease in Gibbs energy;
2) greater loss of Gibbs energy;
3) less loss of Gibbs energy;
4) is equal to the loss of enthalpy.
54 . What conditions must be met so that the maximum work in the system is accomplished due to the decrease in Gibbs energy?
1) it is necessary to maintain constant V and t;
2) it is necessary to maintain constant P and t;
3) it is necessary to maintain constant AH and AS;
4) it is necessary to maintain constant P&V
55 . What causes the maximum useful work done in a chemical reaction at constant pressure and temperature?
1) due to the decrease in Gibbs energy;
3) due to an increase in enthalpy;
4) due to a decrease in entropy.
56. Due to what is the maximum useful work done by a living organism under isobaric-isothermal conditions?
1) due to the loss of enthalpy;
2) due to an increase in entropy;
3) due to the decrease in Gibbs energy;
4) due to an increase in the Gibbs energy.
57 . What processes are called endergonic?
58. What processes are called exergonic?
2) AG 0; 4) AG > 0.
59. The spontaneous nature of the process is best determined by assessing:
1) entropy;
3) enthalpy;
2) Gibbs free energy;
4) temperature.
60 . What thermodynamic function can be used to predict the possibility of spontaneous processes occurring in a living organism?
1) enthalpy;
3) entropy;
2) internal energy;
4) Gibbs free energy.
61 . For reversible processes, the change in Gibbs free energy...
1) always equal to zero;
2) always negative;
3) always positive;
62 . For irreversible processes, the change in free energy:
1) always equal to zero;
2) always negative;
3) always positive;
4) positive or negative depending on the circumstances.
63. Under isobaric-isothermal conditions, only such processes can spontaneously occur in a system, as a result of which the Gibbs energy is:
1) does not change;
2) increases;
3) decreases;
4) reaches its maximum value.
64 . For a certain chemical reaction in the gas phase at constant P and TAG > 0. In what direction does this reaction spontaneously proceed?
D) in the forward direction;
2) cannot occur under these conditions;
3) in the opposite direction;
4) is in a state of equilibrium.
65 . What is the sign AG of the ice melting process at 263 K?
66 . In which of the following cases is the reaction not feasible at any temperature?
1)AH>0;AS>0; 2)AH>0;AH
3)A#4)AH= 0;AS = 0.
67. In which of the following cases is the reaction possible at any temperature?
1)DN 0; 2)AH 0; AS > 0; 4)AH = 0;AS = 0.
68 . If AN
1) [AN] > ;
2) for any ratio of AN and TAS; 3)(AH]
4) [AN] = [T-A S].
69 . At what values of the sign of AH and AS are only exothermic processes possible in the system?
70. At what ratios of AN and T* AS is the chemical process directed towards an endothermic reaction:
71 . At what constant thermodynamic parameters can a change in enthalpy serve as a criterion for the direction of a spontaneous process? What sign of DH under these conditions indicates a spontaneous process?
1) at constant S and P, AN
3) with constant Put, AN
2) at constant 5 and P, AN > 0; 4) at constant Vn t, AH > 0.
72 . Is it possible and in what cases to judge by the sign of the change in enthalpy during a chemical reaction about the possibility of its occurrence at constant Ti P1
1) possible, if LA » T-AS;
2) under these conditions it is impossible;
3) possible, if AN « T-AS;
4) possible if AN = T-AS.
73 . The reaction ZN 2 + N 2 -> 2NH 3 is carried out at 110°C, so that all reactants and products are in the gas phase. Which of the following values is conserved during the reaction?
2) entropy;
3) enthalpy;
74 . Which of the following statements are true for reactions occurring under standard conditions?
1) endothermic reactions cannot occur spontaneously;
2) endothermic reactions can occur at sufficiently low temperatures;
3) endothermic reactions can occur at high temperatures if AS > 0;
4) endothermic reactions can occur at high temperatures if AS
75 . What are the features of biochemical processes: a) obey the principle of energy coupling; b) usually reversible; c) complex; d) only exergonic (AG
1) a, b, c, d;
2) b, c, d; 3) a, 6, c; 4) c, d.
76 . Exergonic reactions in the body occur spontaneously, since:
77 . Endergonic reactions in the body require energy supply, since: 1) AG >0;
78 . When any peptide AH 0 is hydrolyzed, will this process occur spontaneously?
1) will be, since AG > 0;
3) will not happen, since AG > 0;
2) will be, since AG
4) will not be, since AG
79 . The calorie content of nutrients is called energy:
1) 1 g of nutrients released during complete oxidation;
2) 1 mole of nutrients released during complete oxidation;
3) necessary for complete oxidation of 1 g of nutrients;
4) 1 mole of nutrients required for complete oxidation.
80 . For the process of thermal denaturation of many enzymes, LA > 0 and AS > 0. Can this process occur spontaneously?
1) it can at high temperatures, since \T-AS\ > |BP];
2) can at low temperatures, since \T-AS\
3) cannot, since \T-AS\ > |AH];
4) cannot, because \T-AS\
81 . For the process of thermal hydration of many AN proteins
1) can at sufficiently low temperatures, since |AH| > \T-AS\;
2) can at sufficiently low temperatures, since |АА|
3) can at high temperatures, since |AH)
4) cannot at any temperature.
ProgramParameters chemical reactions, chemical equilibrium; - calculate thermal effects and speed chemical reactions... reactions; - basics physical and colloid chemistry, chemical kinetics, electrochemistry, chemical thermodynamics and thermochemistry; ...
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DocumentSimple substances. In this basis V chemical thermodynamics a system for calculating thermal effects has been created..., Cr2O3? TOPIC 2. CHEMICAL KINETICS AND CHEMICAL EQUILIBRIUM As was shown earlier, chemical thermodynamics allows you to predict the fundamental...
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Working programm4.1.5. Redox processes. Basics electrochemistry Oxidation-reduction processes. ... Methods for quantitatively expressing the composition of solutions. 5 Chemical thermodynamics 6 Kinetics And equilibrium. 7 Dissociation, pH, hydrolysis 8 ...
Methodical advice
(L.1, pp. 168-210)
Thermochemistry studies the thermal effects of chemical reactions. Thermochemical calculations are based on the application of Hess's law. Based on this law, it is possible to calculate the thermal effects of reactions using tabular data (Appendix, Table 3). It should be noted that thermochemical tables are usually constructed on the basis of data for simple substances, the heats of formation of which are assumed to be zero.
Thermodynamics develops the general laws of the occurrence of chemical reactions. These patterns can be quantified by the following thermodynamic quantities: internal energy of the system (U), enthalpy (H), entropy (S) and isobaric-isothermal potential (G - Gibbs free energy).
The study of the rate of chemical reactions is called chemical kinetics. The central issues of this topic are the law of mass action and chemical equilibrium. Pay attention to the fact that the study of the rate of chemical reactions and chemical equilibrium is of great importance, since it allows you to control the flow of chemical reactions.
Theoretical aspects
4.1 Chemical thermodynamics
Chemical thermodynamics - the science of the dependence of the direction and limits of transformations of substances on the conditions in which these substances are found.
Unlike other branches of physical chemistry (structure of matter and chemical kinetics), chemical thermodynamics can be applied without knowing anything about the molecular structure of matter. Such a description requires significantly less initial data.
Example:
The enthalpy of glucose formation cannot be determined by direct experiment:
6 C + 6 H 2 + 3 O 2 = C 6 H 12 O 6 (H x -?) such a reaction is impossible
6 CO 2 + 6 H 2 O = C 6 H 12 O 6 + 6 O 2 (H y - ?) the reaction occurs in green leaves, but together with other processes.
Using Hess's law, it is enough to combine three combustion equations:
1) C + O 2 = CO 2 H 1 = -394 kJ
2) H 2 + 1/2 O 2 = H 2 O (steam) H 2 = -242 kJ
3) C 6 H 12 O 6 + 6 O 2 = 6 CO 2 + 6 H 2 O H 3 = -2816 kJ
We add the equations, “expanding” the third, then
H x = 6 H 1 + 6 H 2 - H 3 = 6(-394) + 6(-242) -(-2816) = -1000 kJ/mol
The solution did not use any data on the structure of glucose; The mechanism of its combustion was also not considered.
The isobaric potential is expressed in kJ/mol. Its change during a chemical reaction does not depend on the path of the reaction, but is determined only by the initial and final states of the reacting substances (Hess’s law):
ΔG reaction = Σ ΔG final product - Σ ΔG starting materials
Specific object of thermodynamic research called a thermodynamic system, isolated from the surrounding world by real or imaginary surfaces. A system can be a gas in a vessel, a solution of reagents in a flask, a crystal of a substance, or even a mentally isolated part of these objects.
If the system has real interface, separating parts of the system from each other that differ in properties, then the system is called heterogeneous(saturated solution with sediment), if there are no such surfaces, the system is called homogeneous(true solution). Heterogeneous systems contain at least two phases.
Phase– a set of all homogeneous parts of the system, identical in composition and in all physical and chemical properties (independent of the amount of substance) and delimited from other parts of the system by an interface. Within one phase, properties can change continuously, but at the interface between phases, properties change abruptly.
Components name the substances that are minimally necessary to compose a given system (at least one). The number of components in a system is equal to the number of substances present in it, minus the number of independent equations connecting these substances.
According to the levels of interaction with the environment, thermodynamic systems are usually divided into:
– open – exchange matter and energy with the environment (for example, living objects);
– closed – exchange only energy (for example, a reaction in a closed flask or a flask with reflux), the most common object of chemical thermodynamics;
– isolated – do not exchange either matter or energy and maintain a constant volume (approximation – reaction in a thermostat).
The properties of the system are divided into extensive (summing) - for example, total volume, mass, and intensive (levelling) - pressure, temperature, concentration, etc. The set of properties of a system determines its state. Many properties are interrelated, therefore, for a homogeneous one-component system with a known amount of substance n, it is enough to choose the state to characterize two out of three properties: temperature T, pressure p and volume V. The equation connecting the properties is called the equation of state; for an ideal gas it is:
Laws of thermodynamics
First law of thermodynamics:Energy is neither created nor destroyed. A perpetual motion machine (perpetuum mobile) of the first kind is impossible. In any isolated system the total amount of energy is constant.
In general, the work done by a chemical reaction at constant pressure (isobaric process) consists of a change in internal energy and work of expansion:
For most chemical reactions carried out in open vessels, it is convenient to use state function, the increment of which is equal to the heat received by the system in an isobaric process. This function is called enthalpy(from the Greek “enthalpo” - heat):
Another definition: the enthalpy difference in the two states of the system is equal to the thermal effect of the isobaric process.
There are tables containing data on the standard enthalpies of formation of substances H o 298. The indices mean that for chemical compounds the enthalpy of formation of 1 mole of them from simple substances taken in the most stable modification (except for white phosphorus - not the most stable, but the most reproducible form of phosphorus) at 1 atm (1.01325∙10 5 Pa or 760 mmHg) and 298.15 K (25 o C). If we are talking about ions in solution, then the standard concentration is 1M (1 mol/l).
The sign of enthalpy is determined “from the point of view” of the system itself: when heat is released, the change in enthalpy is negative, when heat is absorbed, the change in enthalpy is positive.
Second law of thermodynamics
Change entropy equal (by definition) to the minimum heat supplied to the system in a reversible (all intermediate states are in equilibrium) isothermal process, divided by the absolute temperature of the process:
S = Q min. /T
At this stage of studying thermodynamics, it should be accepted as a postulate that there is some extensive property of the system S, called entropy, the change of which is so connected with the processes in the system:
In a spontaneous process S > Q min. /T
In the equilibrium process S = Q min. /T
< Q мин. /T
For an isolated system, where dQ = 0, we obtain:
In a spontaneous process S > 0
In the equilibrium process S = 0
In a non-spontaneous process S< 0
In general the entropy of an isolated system either increases or remains constant:
The concept of entropy arose from earlier formulations of the second law (beginning) of thermodynamics. Entropy is a property of the system as a whole, and not of an individual particle.
Third law of thermodynamics (Planck's postulate)
The entropy of a properly formed crystal of a pure substance at absolute zero is zero(Max Planck, 1911). This postulate can be explained by statistical thermodynamics, according to which entropy is a measure of the disorder of a system at the micro level:
S = k b lnW - Boltzmann equation
W is the number of different states of the system available to it under given conditions, or the thermodynamic probability of the macrostate of the system.
k b = R/N A = 1.38. 10 -16 erg/deg – Boltzmann constant
In 1872, L. Boltzmann proposed a statistical formulation of the second law of thermodynamics: an isolated system evolves predominantly in the direction of a higher thermodynamic probability.
The introduction of entropy made it possible to establish criteria that make it possible to determine the direction and depth of any chemical process (for a large number of particles in equilibrium).
Macroscopic systems reach equilibrium when the change in energy is compensated by the entropy component:
At constant volume and temperature:
U v = TS v or (U-TS) = F = 0 - Helmholtz energy or isochoric-isothermal potential
At constant pressure and temperature:
H p = TS p or (H-TS) = G = 0 - Gibbs energy or Gibbs free energy or isobaric-isothermal potential.
Change in Gibbs energy as a criterion for the possibility of a chemical reaction: G =H - TS
At G< 0 реакция возможна;
at G > 0 the reaction is impossible;
at G = 0 the system is in equilibrium.
The possibility of a spontaneous reaction in an isolated system is determined by a combination of the signs of the energy (enthalpy) and entropy factors:
Extensive tabular data are available for standard values of G 0 and S 0 to allow calculation of the G 0 reaction.
If the temperature differs from 298 K and the concentration of reagents from 1M, for the process in general form:
G = G 0 + RT ln([C] c [D] d /[A] a [B] b)
In the equilibrium position G = 0 and G 0 = -RTlnK р, where
K р = [C] c equals [D] d equals /[A] a equals [B] b equals equilibrium constant
K р = exp (-G˚/RT)
Using the above formulas, it is possible to determine the temperature from which the endothermic reaction, at which entropy increases, becomes easily feasible. The temperature is determined from the condition.
1 . What does chemical thermodynamics study:
1) the rate of chemical transformations and the mechanisms of these transformations;
2) energy characteristics of physical and chemical processes and the ability of chemical systems to perform useful work;
3) conditions for shifting chemical equilibrium;
4) the influence of catalysts on the rate of biochemical processes.
2. An open system is a system that:
2) exchanges both matter and energy with the environment;
3. A closed system is a system that:
1) does not exchange either matter or energy with the environment;
3) exchanges energy with the environment, but does not exchange matter;
4) exchanges matter with the environment, but does not exchange energy.
4. An isolated system is a system that:
1) does not exchange either matter or energy with the environment;
2) exchanges both matter and energy with the environment;
3) exchanges energy with the environment, but does not exchange matter;
4) exchanges matter with the environment, but does not exchange energy.
5. To what type of thermodynamic systems does the solution located in a sealed ampoule placed in a thermostat belong?
1) isolated;
2) open;
3) closed;
4) stationary.
6. What type of thermodynamic systems does the solution in the sealed ampoule belong to?
1) isolated;
2) open;
3) closed;
4) stationary.
7. What type of thermodynamic systems does a living cell belong to?
1) open;
2) closed;
3) isolated;
4) equilibrium.
8 . What parameters of a thermodynamic system are called extensive?
1) the magnitude of which does not depend on the number of particles in the system;
2) whose value depends on the number of particles in the system;
3) the value of which depends on the state of aggregation of the system;
9. What parameters of a thermodynamic system are called intensive?
!) the magnitude of which does not depend on the number of particles in the system;
2) the magnitude of which depends on the number of particles in the system;
3) the value of which depends on the state of aggregation;
4) the magnitude of which depends on time.
10 . Functions of the state of a thermodynamic system are quantities that:
1) depend only on the initial and final state of the system;
2) depend on the process path;
3) depend only on the initial state of the system;
4) depend only on the final state of the system.
11 . What quantities are functions of the state of the system: a) internal energy; b) work; c) warmth; d) enthalpy; d) entropy.
1) a, d, e;
3) all quantities;
4) a, b, c, d.
12 . Which of the following properties are intensive: a) density; b) pressure; c) mass; d) temperature; e) enthalpy; e) volume?
1) a, b, d;
3) b, c, d, f;
13. Which of the following properties are extensive: a) density; b) pressure; c) mass; d) temperature; e) enthalpy; e) volume?
1) c, d, f;
3) b, c, d, f;
14 . What forms of energy exchange between the system and the environment are considered by thermodynamics: a) heat; b) work; c) chemical; d) electric; e) mechanical; e) nuclear and solar?
1)a, b;
2) c, d, e, f;
3) a, c, d, e, f;
4) a, c, d, e.
15. Processes occurring at a constant temperature are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
16 . Processes occurring at constant volume are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
17 . Processes occurring at constant pressure are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
18 . The internal energy of the system is: 1) the entire energy reserve of the system, except for the potential energy of its position andkinetic energysystems as a whole;
2) the entire energy reserve of the system;
3) the entire energy reserve of the system, except for the potential energy of its position;
4) a quantity characterizing the degree of disorder in the arrangement of particles of the system.
19 . What law reflects the relationship between work, heat and internal energy of a system?
1) second law of thermodynamics;
2) Hess's law;
3) the first law of thermodynamics;
4) van't Hoff's law.
20 . The first law of thermodynamics reflects the relationship between:
1) work, heat and internal energy;
2) Gibbs free energy, enthalpy and entropy of the system;
3) work and heat of the system;
4) work and internal energy.
21 . Which equation is the mathematical expression of the first law of thermodynamics for isolated systems?
l)AU=0 2)AU=Q-p-AV 3)AG = AH-TAS
22 . Which equation is the mathematical expression of the first law of thermodynamics for closed systems?
2)AU=Q-p-AV;
3) AG = AH - T*AS;
23 . Is the internal energy of an isolated system a constant or variable quantity?
1) constant;
2) variable.
24 . In an isolated system, the reaction of hydrogen combustion occurs with the formation of liquid water. Does the internal energy and enthalpy of the system change?
1) internal energy will not change, enthalpy will change;
2) internal energy will change, enthalpy will not change;
3) internal energy will not change, enthalpy will not change;
4) internal energy will change, enthalpy will change.
25 . Under what conditions is the change in internal energy equal to the heat received by the system from the environment?
1) at constant volume;
3) at constant pressure;
4) under no circumstances.
26 . The thermal effect of a reaction occurring at constant volume is called a change:
1) enthalpy;
2) internal energy;
3) entropy;
4) Gibbs free energy.
27 . The enthalpy of a reaction is:
1) the amount of heat that is released or absorbed during a chemical reaction under isobaric-isothermal conditions;
4) a quantity characterizing the degree of disorder in the arrangement and movement of particles in the system.
28. Chemical processes during which the enthalpy of the system decreases and heat is released into the external environment are called:
1) endothermic;
2) exothermic;
3) exergonic;
4) endergonic.
29 . Under what conditions is the change in enthalpy equal to the heat received by the system from the environment?
1) at constant volume;
2) at constant temperature;
3) at constant pressure;
4) under no circumstances.
30 . The thermal effect of a reaction occurring at constant pressure is called a change:
1) internal energy;
2) none of the previous definitions are correct;
3) enthalpy;
4) entropy.
31. What processes are called endothermic?
1) for which AN is negative;
3) for whichANpositively;
32 . What processes are called exothermic?
1) for whichANnegative;
2) for which AG is negative;
3) for which AN is positive;
4) for which AG is positive.
33 . Specify the formulation of Hess's law:
1) the thermal effect of the reaction depends only on the initial and final state of the system and does not depend on the reaction path;
2) the heat absorbed by the system at a constant volume is equal to the change in the internal energy of the system;
3) the heat absorbed by the system at constant pressure is equal to the change in enthalpy of the system;
4) the thermal effect of the reaction does not depend on the initial and final state of the system, but depends on the reaction path.
34. What law underlies the calculation of caloric content of food?
1) van't Hoff;
2) Hess;
3) Sechenov;
35. When oxidizing which substances under body conditions, more energy is released?
1) proteins;
2) fat;
3) carbohydrates;
4) carbohydrates and proteins.
36 . A spontaneous process is a process that:
1) carried out without the help of a catalyst;
2) accompanied by the release of heat;
3) carried out without external energy consumption;
4) proceeds quickly.
37 . Entropy of a reaction is:
1) the amount of heat that is released or absorbed during a chemical reaction under isobaric-isothermal conditions;
2) the amount of heat that is released or absorbed during a chemical reaction under isochoric-isothermal conditions;
3) a value characterizing the possibility of spontaneous occurrence of the process;
4) a quantity characterizing the degree of disorder in the arrangement and movement of particles in a system.
38 . What state function characterizes the tendency of a system to achieve a probable state that corresponds to the maximum randomness of the distribution of particles?
1) enthalpy;
2) entropy;
3) Gibbs energy;
4) internal energy.
39 . What is the relationship between the entropies of three aggregate states of one substance: gas, liquid, solid:
I) S(d) >S(g) >S(TV); 2) S(solid)>S(g)>S(g); 3)S(g)>S(g)>S(TB); 4) the state of aggregation does not affect the entropy value.
40 . Which of the following processes should exhibit the greatest positive change in entropy:
1) CH3OH (s) --> CH,OH (g);
2) CH3OH (s) --> CH 3 OH (l);
3) CH,OH (g) -> CH3OH (s);
4) CH,OH (l) -> CH3OH (sol).
41 . Choose the correct statement: the entropy of the system increases when:
1) increased pressure;
2) transition from liquid to solid state of aggregation
3) temperature increase;
4) transition from gaseous to liquid state.
42. What thermodynamic function can be used to predict whether a reaction will occur spontaneously in an isolated system?
1) enthalpy;
2) internal energy;
3) entropy;
4) potential energy of the system.
43 . Which equation is the mathematical expression of the 2nd law of thermodynamics for isolated systems?
2)AS>Q\T
44 . If the system reversibly receives an amount of heat Q at temperature T, then about T;
2) increases by the amountQ/ T;
3) increases by an amount greater than Q/T;
4) increases by an amount less than Q/T.
45 . In an isolated system, a chemical reaction occurs spontaneously to form a certain amount of product. How does the entropy of such a system change?
1) increases
2) decreases
3) does not change
4) reaches the minimum value
46 . Indicate in which processes and under what conditions the change in entropy can be equal to the work of the process?
1) in isobaric conditions, at constant P and T;
2) in isochoric, at constant Vi and T;
H) the change in entropy is never equal to work;
4) in isothermal conditions, at constant P and 47 . How will the bound energy of the system TS change when heated and when it condenses?
