Topic. The rate of chemical reactions
1. Gas A was mixed in a vessel with a quantity of substance 4.5 mol and gas B with a quantity of substance 3 mol. Gases A and B react in accordance with the equation A + B \u003d C. After some time, gas C was formed in the system with a substance of 2 mol. What quantities of unreacted gases A and B remained in the system?
It follows from the reaction equation that:
Dn(A) = Dn(B) = Dn(C) = 2 mol,
where Dn is the change in the amount of a substance during the reaction.
Therefore, in the vessel remains:
n 2 (A) = n 1 (A) - Dn(A); n 2 (A) \u003d (4.5 - 2) mol \u003d 2.5 mol;
n 2 (B) = n 1 (B) - Dn(B); n 2 (B) \u003d (3 - 2) mol \u003d 1 mol.
2. The reaction proceeds according to the equation: 2A + B ⇄ C and has the second order for substance A and the first for substance B. At the initial moment of time, the reaction rate is 15 mol/l×s. Calculate the rate constant and the rate of the direct reaction at the moment when 50% of substance B reacts, if the initial concentrations are equal: С(A) = 10 mol/l; C(B) = 5 mol/l. How will the rate of a chemical reaction change?
С(B), which has entered into the reaction, is equal to:
C(B) \u003d 0.5 5 \u003d 2.5 mol / l.
Accordingly, C(A), which has entered into the reaction, is equal to:
2 mol/l A - 1 mol/l B
C(A) - 2.5 mol/l B
C(A) and C(B) after the reaction:
C(A) \u003d 10 - 5 \u003d 5 mol / l,
C(B) \u003d 5 - 2.5 \u003d 2.5 mol / l.
The rate of the direct reaction will be:
The rate of a chemical reaction will change:
i.e., it will decrease by 8 times.
3. The reaction between substances A and B is expressed by the equation: A + 2B \u003d C and has the first order in substance A and the second in substance B. The initial concentrations of substances are: C (A) \u003d 2 mol / l; C(B) = 4 mol/l; the rate constant is 1.0. Find the initial rate of the reaction and the rate after some time, when the concentration of substance A decreases by 0.3 mol/l.
According to the law of mass action:
If the concentration of substance A decreases by 0.3 mol/l, then the concentration of substance B will decrease by 0.3 × 2 = 0.6 mol/l. After the reaction, the concentrations are:
4. The rates of direct and reverse gas-phase reactions occurring in a closed vessel are expressed by the equations:
According to the law of mass action, the rates of direct and reverse reactions under initial conditions are:
An increase in pressure by a factor of 3 for gaseous systems leads to a decrease in the volume of the gas mixture by a factor of 3, the concentrations of all three gases will increase by the same amount, and the rates of both reactions will become respectively equal:
The reaction rate ratios are:
Thus, the rate of the forward reaction will increase by 27 times, the reverse - by 9.
5. The reaction at a temperature of 50 0 C proceeds in 2 minutes 15 seconds. How long will it take for this reaction to end at a temperature of 70 0 C, if the temperature coefficient of the rate g is 3 in this temperature range?
With an increase in temperature from 50 to 70 0 C, the reaction rate increases in accordance with the van't Hoff rule:
where = 70 0 C, \u003d 50 0 С, a and - reaction rates at given temperatures.
We get:
those. the reaction rate increases by 9 times.
According to the definition, the reaction time is inversely proportional to the rate of the reaction, therefore:
where and is the reaction time at temperatures And .
From here we get:
Given that = 135 s (2 min 15 s), we determine the reaction time at a temperature :
6. How many times will the rate of a chemical reaction increase with an increase in temperature from = 10 0 C to = 80 0 С , if the temperature coefficient of speed g is equal to 2?
From the van't Hoff rule:
The reaction rate will increase 128 times.
7. When studying the kinetics of drug excretion from the patient's body, it was found that in 3 hours 50% of the initial amount of the drug remained in the patient's body. Determine the half-life and rate constant of the elimination reaction of the drug from the human body, if it is known that this is a first-order reaction.
Since for a given period of time 50% of the drug was removed from the body, then t 1/2 = 3 hours. We calculate the reaction rate constant from the equation:
8. In laboratory studies of aqueous solutions of the drug, it was found that due to hydrolysis, the concentration of the drug per day decreased from 0.05 mol/l to 0.03 mol/l. Calculate the half-life of the hydrolysis reaction of the drug.
Since hydrolysis reactions usually proceed with a significant excess of water, its concentration can be constant. Consequently, only the concentration of the drug changes during the reaction, and the hydrolysis reaction can be considered a first-order reaction.
We find the value of the reaction rate constant from the equation:
9. The half-life of the drug from the patient's body (first-order reaction) is 5 hours. Determine the time during which 75% of the drug will be removed from the body.
With the removal of 75% of the drug from the body, the C / C 0 ratio will be 0.25. In this case, it is convenient to use the formula:
,
10. The rate constant of the sucrose hydrolysis reaction is 2.31×10 - 3 h - 1 . Calculate:
1) the half-life of the reaction;
2) the time during which 20% of sucrose undergoes hydrolysis;
3) what part of glucose will undergo hydrolysis after 5 days.
1. The half-life is:
2. After 20% of sucrose has undergone hydrolysis, the C/C 0 ratio will be 0.8. Consequently:
3. After 5 days (120 hours), the C / C 0 ratio will be:
Consequently, 24% of glucose underwent hydrolysis.
11. In the course of some first-order reaction, 60% of the initial amount of the substance is converted in 30 minutes. Determine what part of the substance will remain after 1 hour.
1. After 30 minutes, the amount of the remaining substance will be:
C 1 \u003d C 0 - 0.6 C 0 \u003d 0.4 × C 0.
i.e., the C 0 /C 1 ratio is 2.5.
2. Find the reaction rate constant:
3. The amount of substance C 2 remaining after 1 hour is determined by the formula:
Thus, after 1 hour, 16% of the original substance will remain.
Questions for self-control
1. What is called the rate of a chemical reaction?
2. What is called the true rate of a homogeneous reaction?
3. What is the dimension of the rate of a homogeneous reaction?
4. What is called the rate of a heterogeneous reaction?
5. What is the dimension of the rate of a heterogeneous reaction?
6. List the factors that affect the reaction rate.
7. Formulate the law of mass action.
8. What is the physical meaning of the reaction rate constant? What does the rate constant of a reaction depend on and what does it not depend on?
9. What is called the reaction order? Give examples of reaction equations of zero, first, second and third orders.
10. Does the dimension of the reaction rate constant depend on the order of the reaction?
11. What is called the molecularity of the reaction?
13. Define simple and complex reactions. Give a classification of complex reactions.
14. Formulate the van't Hoff rule. Give a mathematical expression for the van't Hoff rule.
15. How does the reaction rate depend on the activation energy? Write the Arrhenius equation.
16. What is an activated complex? Why do reactions proceed through the stages of formation of activated complexes?
17. What is called a catalyst? Homogeneous and heterogeneous catalysis. Why do reactions proceed faster in the presence of catalysts?
18. What is enzymatic catalysis? Write the Michaelis-Menten equation.
Variants of tasks for independent solution
Option number 1
1. The reaction between substances A and B is expressed by the equation 2A + B \u003d C and has the second order for substance A and the first for substance B. The initial concentrations of substances are: C 0 (A) \u003d 0.4 mol / l; C 0 (B) \u003d 0.8 mol / l; k = 0.6. Find the initial rate of the reaction and the rate after some time, when the concentration of substance A decreases by 0.2 mol/l.
2. By how many degrees should the temperature be raised so that the reaction rate increases by 64 times? The temperature coefficient of the reaction rate g is 2.
a) when the pressure in the system doubles?
b) with an increase in the volume of gases by 2 times?
Option number 2
1. The reaction proceeds according to the equation: A + B = C and has the first order in substance A and in substance B. The concentration of A was increased from 2 to 8 mol/l, and the concentration of B from 3 to 9 mol/l. By how much did the rate of the forward reaction increase?
2. At 150 0 C, the reaction ends in 10 minutes. Taking the temperature coefficient g equal to 2, calculate how many minutes the reaction would have ended at 170 0 C.
3. The reaction rate is expressed by the equation: 
How many times will the reaction rate change when the concentration of the starting substances is increased by 3 times?
Option number 3
1. The reaction is expressed by the equation: A + B \u003d C and has the first order in substance A and in substance B. At initial concentrations C 0 (A) \u003d 3 mol / l and C 0 (B) \u003d 5 mol / l, the rate of the direct reaction equal to 0.3 mol/l×s. Determine the rate constant and the reaction rate after some time, when the concentration of A decreases by 2 mol/L.
2. How many times will the rate of a chemical reaction increase with an increase in temperature from 10 to 70 0 C, if the temperature coefficient of the rate g is 2?
3. The reaction rate A (tv) + 2B (gas) = C (tv) is expressed by the equation: 
How will the reaction rate change if the concentration of B is doubled?
Option number 4
1. The reaction proceeds according to the equation: 2A + B = 2C and has the second order for substance A and the first for substance B. Calculate the rate of the direct reaction at the moment when 40% of substance B reacts if the initial concentrations are: C 0 (A) = 8 mol/l; C 0 (B) = 4 mol/l; k = 0.4.
2. Some reaction at 100 0 C ends in 5 minutes. How long will it take to end at 80 0 C if the temperature coefficient of velocity g is 3?
3. The reaction rate 3A + B = C is expressed by the equation: 
How many times will the rate of the direct reaction change?
a) when the concentration of substance A is doubled?
b) with a simultaneous decrease in the concentration of the starting substances by 2 times?
Option number 5
1. The rate of a certain reaction with an increase in temperature from 40 to 70 0 C increased by 8 times. Determine the value of g.
2. The reaction proceeds according to the equation: A + 3B = 2C and has the first order for substance A and the second for substance B. The initial concentrations of substances are: C 0 (A) = 2 mol / l; C 0 (B) = 6 mol/l; k = 1. Calculate the initial rate of the forward reaction and the rate at the moment when the concentration of substance A decreased by 1 mol/l. How will the rate of a chemical reaction change?
3. How will the rates of direct and reverse reactions occurring in the gas phase and obeying the equations change:
Option number 6
1. In a closed vessel there is a mixture of gases, consisting of 1 mol A and 3 mol B, which reacts according to the equation: A + 3B = 2C. The rate of the direct reaction is described by the equation 
How many times will the rate of the direct reaction decrease after 0.5 mol A has reacted?
2. By how many degrees should the temperature be increased so that the reaction rate increases by 9 times if the temperature coefficient of the rate g is 3?
3. How will the rate of the direct gas-phase reaction change: 2A = B, the order of which is estimated as 0.5, with an isothermal decrease in pressure in the system by 3 times?
Option number 7
1. The reaction between substances A and B proceeds according to the equation: A + 2B \u003d C and has the first order in substance A and in substance B. The initial concentrations of the reactants were: C 0 (A) \u003d 1.5 mol / l; C 0 (B) = 3 mol/l; k = 0.4. Calculate the rate of a chemical reaction at the initial moment of time and after some time, when 75% A has reacted.
2. What is the temperature coefficient of the rate g if, with an increase in temperature by 30 0 C, the reaction rate increases by 27 times?
3. How will the rates of direct and reverse reactions occurring in the gas phase and obeying the equations change:
with an isothermal increase in pressure by 2 times?
Option number 8
1. In a 1 liter solution containing 1 mol of substance A and 2 mol of substance B, the reaction proceeds: A + 3B \u003d 2C + D. The direct reaction has the first order for substance A and the second for substance B. How many times will the speed of the direct decrease reaction after 0.65 mol of substance A?
2. When the temperature rises from -5 to +5 0 C, the rate of bacterial hydrolysis (enzymatic process) increases by 4 times. Find the value of the temperature coefficient of the reaction rate g.
3. How many times should the concentration of substance A be increased in the system 2A (gas) \u003d B (gas) + C (solid) so that the rate of the direct reaction, which is a second-order reaction, increases by 4 times?
Option number 9
1. The reaction proceeds according to the equation: 2A + B = 2C and has the second order for substance A and the first for substance B. The rate of the direct reaction is 8 mol/l×s. Calculate the rate constant and the rate of the direct reaction at the moment when 30% of substance B reacts if the initial concentrations are: C 0 (A) = 2 mol/l; C 0 (B) \u003d 1 mol / l. How will the rate of a chemical reaction change?
2. With an increase in temperature from 10 to 50 0 C, the reaction rate increased by 16 times. Determine the temperature coefficient of velocity g.
3. The reaction proceeds according to the equation: A + B = C + D + E and has the first order for substance A and zero for substance B. How will the rate of the direct reaction change after diluting the reacting mixture by 3 times?
Option number 10
1. The reaction proceeds according to the equation: A + 2B \u003d AB 2 and has the first order in substance A and the second in substance B. The reaction rate constant is 0.01. Calculate the reaction rate at initial concentrations: C 0 (A) = 0.8 mol/l; C 0 (B) \u003d 0.8 mol / l and the reaction rate at the time of formation of 0.2 mol / l of substance AB 2.
2. How many times will the rate of a chemical reaction increase with an increase in temperature from 30 to 60 0 C, if the temperature coefficient of the rate g is 3?
3. The half-life of the drug from the patient's body (first-order reaction) is 6 hours. Determine the time for which the content of the drug in the human body will decrease by 8 times.
Option number 11
1. The reaction proceeds according to the equation: A + B \u003d 2C and has the first order in substance A and in substance B. The initial concentrations of substances are: C 0 (A) \u003d 0.3 mol / l; C 0 (B) \u003d 0.5 mol / l; k = 0.1. Find the initial reaction rate and the reaction rate after some time, when the concentration A decreases by 0.1 mol/l.
2. At 100 0 C, some reaction ends in 16 minutes. Taking the temperature coefficient of the rate g equal to 2, calculate in how many minutes the same reaction would have ended at 140 0 C?
3. The half-life of the drug from the patient's body (first-order reaction) is 2 hours. Determine the time during which 99% of the drug will be removed from the body.
Option number 12
1. The reaction proceeds according to the equation: A + 2B \u003d C and has the first order for substance A and the second for substance B. The initial concentrations of substances are: C 0 (A) \u003d 0.9 mol / l; C 0 (B) \u003d 1.5 mol / l; k = 0.6. Find the initial rate of the reaction and the rate after some time, when 50% of substance A has been consumed.
2. What is the temperature coefficient of the chemical reaction rate g , if with an increase in temperature by 30 0 C, the speed increases by 27 times?
3. The half-life of some first-order reaction is 30 minutes. Calculate what part of the original amount will remain after 1 hour.
Option number 13
1. The reaction proceeds according to the equation: 2A + B = 2C and has the second order for substance A and the first for substance B. The reaction rate constant is 5 × 10 - 2. Calculate the reaction rate at initial concentrations C 0 (A) = 0.4 mol/l; C 0 (B) \u003d 0.9 mol / l and the reaction rate by the time 0.1 mol of substance C is formed.
2. At a temperature of 10 0 C, the reaction proceeds in 80 minutes. At what temperature will the reaction be completed in 20 minutes if the temperature coefficient of the rate g is 2?
3. In the course of laboratory studies, it was found that during the day the concentration of the drug in the patient's body decreased from 0.1 mol/l to 0.02 mol/l. Calculate the half-life of the drug, assuming that this reaction is of the first order.
Option number 14
1. In a closed vessel with a volume of 1 l there is a mixture of gases, consisting of 1 mol of gas A and 3 mol of gas B, which reacts according to the equation: A + 3B = 2C. The direct reaction has the first order in substance A and the second in substance B. How will the rate of the direct reaction change after 0.5 mol of gas A has reacted?
2. With an increase in the temperature of the system from 10 to 50 0 C, the rate of the chemical reaction increased by 16 times. Determine the temperature coefficient of the reaction rate g .
3. During the accident at the Chernobyl nuclear power plant (1986), the radionuclide Cs-137 was released, the half-life of which is 30 years. Calculate what part of the radionuclide that has entered the body has remained at the present time.
Option number 15
1. The reaction proceeds according to the equation: A + B \u003d C has the first order in substance A and in substance B. At initial concentrations of substances C 0 (A) \u003d 0.6 mol / l; C 0 (B) = 0.8 mol/l, the reaction rate is 0.03 mol/l×s. Determine the rate constant and the reaction rate after some time, when the concentration of substance A decreases by 0.3 mol/l.
2. The reaction rate at 0 0 C is 1 mol/l×s. Calculate the rate of this reaction at 30 0 C if the temperature coefficient of the reaction rate is 3.
3. The rate constant of pesticide hydrolysis at 25 0 C is 0.32 s - 1 . The initial concentration of the pesticide in the sample was 2.5 mol/l. Calculate the time it takes for the pesticide concentration to drop to 0.01 mol/L.
Option number 16
1. The decomposition reaction proceeds according to the equation: 2A \u003d 2B + C and has the second order in substance A. The rate constant of this reaction at 200 0 C is 0.05. Initial concentration С(A) = 2 mol/l. Determine the reaction rate at the indicated temperature at the initial moment and at the moment when 80% of substance A has decomposed.
2. How will the rate of the direct reaction change: 2A (tv) + 3B (gas) = 2C (tv), which has a zero order for substance A and the third order for substance B, if the pressure in the system is increased by 3 times?
3. In the course of some first-order reaction, 20% of the initial amount of the substance undergoes transformation in 45 minutes. Determine what part of the substance will remain after 1.5 hours.
Option number 17
1. The interaction of gases proceeds according to the equation: A + 2B = 2C and has the first order in substance A and the second in substance B. The initial concentrations of gases are: C 0 (A) = 2 mol / l; C 0 (B) = 4 mol/l; k = 0.02. Calculate the rate of the direct reaction at the initial moment of time and after some time, when 50% of substance A has reacted.
2. At 20 0 C, the reaction proceeds in 2 minutes. How long will the same reaction take at 0 0 C if g = 2?
3. Formic acid decomposes into carbon monoxide (IV) and hydrogen on the surface of gold. The rate constant of this reaction at 140 0 C is 5.5×10 - 4 min -1 , and at 185 0 C it is 9.2 × 10 - 3 min -1 . Determine the activation energy of this reaction.
Option number 18
1. The reaction proceeds according to the equation: 2A + B = 2C and has the first order in substance A and in substance B. The reaction rate is 0.5 mol/l×s. The initial concentrations of substances are equal: С(A) = 6 mol/l; C(B) = 3 mol/l. Determine the rate constant of this reaction and the rate of the reaction after some time, when the concentration of substance B decreases by 1 mol/l.
2. At 20 0 C, the reaction proceeds in 2 minutes. How long will the same reaction take at 50 0 C if g = 2?
3. The rate constant of the cane sugar inversion reaction at 25 0 C is 9.67×10 - 3 min - 1 , and at 40 0 C it is 73.4 × 10 - 3 min -1 . Determine the activation energy of this reaction in the specified temperature range.
Example 1. The reaction between substances A and B proceeds according to the equation 2A + B = C, the concentrations of substances (mol / l) are [A] = 6, [B] = 5. The reaction rate constant is 0.5 l 2 × mol -2 × s -one . Calculate the rate of the chemical reaction at the initial moment and at the moment when 45% of substance B remains in the reaction mixture.
Solution. According to the law of mass action, the rate of a chemical reaction is directly proportional to the product of the concentrations of reactants in powers equal to the stoichiometric coefficients in the reaction equation. Therefore, for the reaction 2A + B C
V = k C A 2 C B.
The rate of a chemical reaction at the initial moment is:
V 1 = 0.5 6 2 5 \u003d 90 mol s -1 l -1.
If the concentration of at least one of the reacting substances changes, then the concentration of all other substances will also change:
After some time, 45% of substance B remains in the reaction mixture, i.e. [B] \u003d 5 0.45 \u003d 2.25 mol / l. This means that the concentration of substance B decreased by 5.0 - 2.25 = 2.75 mol / l. Since substances A and B interact with each other in a ratio of 2: 1, the concentration of substance A decreased by 5.5 mol (2.752) and became equal to 0.5 mol / l (6.0 - 5.5). Consequently,
V 2\u003d 0.5 ∙ (0.5) 2 2.25 \u003d 0.28 mol s -1 l -1.
Example 2. Determine how the rate of the forward reaction will change
2CO (g) + O 2 (g) \u003d 2CO 2 (g), if the total pressure in the system is increased by 4 times.
Solution. An increase in pressure in the system by 4 times will cause a decrease in the volume of the system by 4 times, and the concentrations of reactants will increase by 4 times. According to the law of mass action, the initial reaction rate is
After increasing the pressure
Therefore, after increasing the pressure by 4 times, the reaction rate increased by 64 times.
Note. The law of action of masses in its classical form (expressed in terms of concentrations) is valid for non-electrolytes and dilute solutions of weak electrolytes (i.e. for gases and solutions). Solid substances are not included in the expression for the reaction rate, since the concept of concentration is unacceptable for them; the rate of reactions in the solid phase depends on the surface area of the solid, i.e. its degree of refinement.
So, for the reaction C (t) + CO 2 (g) \u003d 2CO (g), the rate of the direct reverse reaction.
A change in pressure shifts the equilibrium if the number of moles of the initial and resulting gaseous substances is not the same. For the reaction 2CO + O 2 \u003d 2CO 2, the rate of the forward reaction, reverse.
Example 3. In the system A (g) + 2B (g) \u003d C (g), the equilibrium concentrations are: [A] \u003d 0.06 mol / l; [B]=0.12 mol/l; [C] = 0.216 mol/l. Find the equilibrium constant of the reaction and the initial concentrations of substances A and B.
Solution. According to the law of mass action, the equilibrium constant of this reaction is expressed by the equation
Substituting the task data into it, we get:
According to the reaction equation, 1 mol C is formed from 1 mol A and 2 mol B. Since, according to the condition of the problem, 0.216 mol of substance C was formed in each liter of the system, 0.216 mol A and 0.216 2 = 0.432 mol B were consumed. Thus , the desired initial concentrations are equal to:
[A] \u003d 0.06 + 0.116 \u003d 0.276 mol / l;
[B] \u003d 0.12 + 0.432 \u003d 0.552 mol / l.
Example 4 The reaction proceeds according to the equation A + B = 2C. Determine the equilibrium concentrations of the reactants if the initial concentrations of substances A and B are 0.5 and 0.7 mol/l, respectively, and the equilibrium constant of the reaction TO p = 50.
Solution. By the time of equilibrium, the concentrations of the starting materials A and B will decrease, and the concentration of the reaction product C will increase. For every mole of substances A and B, 2 moles of substance C are formed; therefore, if the decrease in the concentration of substances A and B is denoted by X mol, then the increase in the concentration of substance C will be equal to 2 X mol.
The equilibrium concentrations of the reactants will be:
[A] = (0.5 - X) mol/l; [V] = (0.7 - X) mol/l; [C] = 2 X mol/l.
46x 2 - 60x + 17,5=0.
Solving the equation, we get: x 1 = 0,86; x 2= 0.44. According to the condition of the problem, the value x 2 . Hence, the equilibrium concentrations of the reactants are: [А] = 0.5 – 0.44 = 0.06 mol/l; [B] = 0.7 - 0.44 = = 0.26 mol/l; [C] \u003d 0.44 2 \u003d 0.88 mol / l.
Example 5. Calculate how many times the rate of a chemical reaction will increase with an increase in temperature by 40 ° C if the temperature coefficient of this reaction is 3.
Solution. The dependence of the rate of a chemical reaction on temperature is expressed by the van't Hoff rule of thumb.
In this example, the temperature has risen by 40°C,
Consequently, the reaction rate increased by 3 4 = 81 times.
Questions for self-study
1. Formulate the law of mass action, Van't Hoff's law, Le Chatelier's principle.
2. Name the factors that affect the reaction rate.
3. What is called the equilibrium constant, what does it depend on and what does it characterize?
4. The reaction proceeds according to the equation 4HCI (g) + O 2 (g) \u003d 2H 2 O (g) + 2CI 2 (g). How will the reaction rate change if the pressure in the system is increased by 3 times?
5. How many times should the concentration of hydrogen be increased so that the rate of the reaction N 2 (g) + 3H 2 (g) ® 2NH 3 (g) increases 1000 times? How should the pressure be changed to achieve the same acceleration of the reaction?
6. In which direction does the equilibrium shift: a) with an increase in temperature; b) with increasing pressure:
2H 2 (g) + O 2 (g) ⇆2H 2 O (steam) + 249.9 kJ
2SO 2 (g) + O 2 (g) ⇆2SO 3 (g) + 198.4 kJ
7. The equilibrium of the system 2NO (g) + O 2 (g) ® 2NO 2 (g) was established at the following concentrations of substances: = 0.08 mol / l; = 0.03 mol/l; = 0.01 mol/l. Calculate the equilibrium constant and the initial concentrations of NO and O 2 if the initial concentration of NO 2 is zero.
1. How will the rate of the direct reaction A (g) + 2B (g) → AB 2 change if the pressure in the system is increased by 4 times?
a) the speed will decrease by 10 times;
b) the speed will not change;
c) the speed will increase by 16 times;
d) the speed will increase by 64 times.
2. The temperature coefficient of the rate of some reaction is 2.0. How will the rate of this reaction change if it is lowered by 40 degrees?
a) will increase by 8 times;
b) decrease by 8;
c) will decrease by 16 times;
d) will increase by 16 times.
3. In a homogeneous system A + B = 2C, the equilibrium concentrations of the reacting gases (mol/l): [A] = 0.06; [V] = 0.2; [C] = 0.8. Calculate the equilibrium constant of the system.
4. For the reaction NO (g) + O 2 (g) \u003d NO 2 (g) at 25 ° C Cr= 0.1. What is the ∆G of the reaction?
a) 23.5 kJ/mol;
b) -5.7 J/mol;
c) -44.8 kJ/mol;
d) 22.44 kJ/mol.
5. In what direction will the equilibrium shift as the temperature drops in the reaction:
C 2 H 4 (g) + 3O 2 (g) \u003d 2CO 2 (g) + 2H 2 O (g) (∆H o \u003d -1323 kJ ) ?
a) move to the right
b) shift to the left;
c) the balance will not change.
irreversible reactions
1. How will the reaction rate 2A + B ® A 2 B change if the concentration of substance A is increased by 2 times, and the concentration of substance B is reduced by 2 times?
2. How many times should the concentration of substance B 2 be increased in the system 2A 2 (g) + B 2 (g) ® 2A 2 B (g), so that when the concentration of substance A decreases by 4 times, the rate of the direct reaction does not change?
3. In the system CO + C1 2 ® COS1 2, the concentration of CO was increased from 0.03 to 0.12 mol/l, and the concentration of C1 2 - from 0.02 to 0.06 mol/l. By how much did the rate of the forward reaction increase?
4. How will the rate of the direct reaction N 2 (g) + 3H (g) ® 2 NH 3 change if a) the pressure in the system is increased by 3 times; b) reduce the volume by 2 times; c) increase the concentration of N 2 by 4 times?
5. How many times should the pressure be increased so that the rate of formation of NO 2 by the reaction 2NO + O 2 ® 2 NO 2 increases 1000 times?
6. The reaction between carbon monoxide (II) and chlorine proceeds according to the equation CO + C1 2 ® COC1 2. How will the reaction rate change with an increase in a) CO concentration by 2 times; b) the concentration of C1 2 in 2 times; c) the concentration of both substances is 2 times?
7. The reaction takes place in the gas phase. Two substances A and B participate in the reaction. It is known that with a 2-fold increase in the concentration of component A, the rate increased by 2 times, and with an increase in the concentration of component B by 2 times, the rate increased by 4 times. Write an equation for the ongoing reaction. How will the reaction rate change when the total pressure is increased by 3 times?
8. The reaction rate of the interaction of substances A, B and D is being studied. At constant concentrations B and D, an increase in the concentration of substance A by 4 times leads to an increase in the rate by 16 times. If the concentration of substance B increases by 2 times at constant concentrations of substances A and D, then the speed increases only 2 times. At constant concentrations of A and B, doubling the concentration of substance D leads to a 4-fold increase in speed. Write an equation for the reaction.
9. Determine the rate of the chemical reaction A(g) + B(g) ® AB(g), if the reaction rate constant is 2 × 10 -1 l × mol -1 × s, and the concentrations of substances A and B are respectively 0.025 and 0 .01 mol/l. Calculate the rate of reaction when the pressure is increased by 3 times.
10. Find the value of the rate constant of the reaction A + 2B ® AB 2, if at concentrations of substances A and B, respectively, equal to 0.1 and 0.05 mol / l, the reaction rate is 7 × 10 -5 mol / (l × s) .
11. In a vessel with a volume of 2 l, gas A was mixed with a quantity of substance 4.5 mol and gas B with a quantity of substance 3 mol. Gases react in accordance with the equation A + B = C. After 20 seconds, gas C was formed in the system with a substance of 2 mol. Determine the average rate of the reaction. What amounts of substances A and B did not react?
12. The reaction between substances A and B is expressed by the equation A + B ® C. The initial concentrations are [A] O = 0.03 mol / l, [B] O = 0.05 mol / l. The reaction rate constant is 0.4. Find the initial reaction rate and the reaction rate after some time, when the concentration of the formed substance C becomes equal to 0.01 mol/l.
13. The reaction between gaseous substances A and B is expressed by the equation A + B ® C. The initial concentrations of substances are [A] 0 = 0.03 mol / l, [B] 0 = 0.03 mol / l. The reaction rate constant is 0.1. After some time, the concentration of substance A decreased by 0.015 mol/l. How many times must the total pressure be increased in order for the rate of a chemical reaction to become equal to the initial rate?
14. By how many degrees should the temperature be increased in order for the reaction rate to increase by 27 times? The temperature coefficient of the reaction rate is 3.
15. At 20°C, the reaction proceeds in 2 minutes. How long will this reaction take a) at 50 o C, b) at 0 o C? The temperature coefficient of the reaction rate is 2.
16. At a temperature of 30 o C, the reaction proceeds in 25 minutes, and at 50 o C in 4 minutes. Calculate the temperature coefficient of the reaction rate.
17. The reaction rate at 0 o C is 1 mol / l × s. Calculate the rate of this reaction at 30°C if the temperature coefficient of the rate is 3.
18. With an increase in temperature by 50 ° C, the reaction rate increased by 32 times. Calculate the temperature coefficient of the rate of a chemical reaction.
19. Two reactions proceed at 25 o C at the same rate. The temperature coefficient of the rate of the first reaction is 2.0, and the second - 2.5. Find the ratio of the rates of these reactions at 95 o C.
20. What is the activation energy of the reaction if, as the temperature rises from 290 to 300 K, the reaction rate doubles?
21. How many times will the rate of a reaction occurring at 298 K increase if, as a result of using a catalyst, it was possible to reduce the activation energy by 4 kJ / mol?
22. What is the value of the activation energy of the reaction, the rate of which at 300 K is 10 times greater than at 280 K.
23. The activation energy of the reaction O 3 (g) + NO (g) ® O 2 (g) + NO 2 (g) is 40 kJ / mol. How many times will the reaction rate change with an increase in temperature from 27 to 37 ° C?
24. One catalyst reduces the activation energy at 300 K by 20 kJ/mol, and the other by 40 kJ/mol. Which catalyst is more efficient? Justify your answer by calculating the ratio of reaction rates when using one or another catalyst.
25. At 150°C, some reaction is complete in 16 minutes. Taking the temperature coefficient of the reaction rate equal to 2.5, calculate how long this reaction will end if it is carried out a) at 200 o C, b) at 80 o C.
26. When the temperature rises by 10 ° C, the rate of a chemical reaction increases by 2 times. At 20 about With it is equal to 0.04 mol/(l×s). What will be the rate of this reaction at a) 40 o C, b) 0 o C?
27. At 20 ° C, the rate of a chemical reaction is 0.04 mol / (l × s). Calculate the rate of this reaction at 70°C if the activation energy is known to be 70 kJ/mol.
28. Calculate the temperature coefficient of the reaction g, if the rate constant of this reaction at 120 ° C is 5.88 × 10 -4, and at 170 ° C - 6.7 × 10 -2.
29. How many times will the rate of a chemical reaction change with increasing temperature from 300 K to 400 K if the temperature coefficient g = 2? What is the activation energy for this reaction?
30. How many times will the rate of the chemical reaction A + 2B ® C increase with an increase in pressure in the system by 4 times and a simultaneous increase in temperature by 40 ° C. The reacting substances are gases. The temperature coefficient of the reaction is 2.
31. How many times will the rate of the chemical reaction 2A(g) + B(g) ® 2C(g) decrease when the pressure of all substances in the system is reduced by 3 times and the system temperature is simultaneously lowered by 30 o C? The temperature coefficient of the reaction rate g is 2.
32. The reaction between gaseous substances A and B is expressed by the equation A + B ® C. The initial concentrations of substances are [A] 0 = 0.05 mol / l and [B] 0 = 0.05 mol / l. After some time, the concentration of substances decreased by half. Determine how it is necessary to change the temperature so that the reaction rate becomes equal to the initial rate, if a) the temperature coefficient of the reaction is 2, b) the activation energy is 70 kJ, the reaction temperature is 27 ° C?
33. It is known that when the temperature rises from 290 to 300 K, the rate of a chemical reaction doubles. Calculate the activation energy. How will the rate of this reaction change at 310 K if a catalyst is introduced into the system that lowers the activation energy of this reaction by 10 kJ/mol?
Chemical equilibrium
1. At a certain temperature, the equilibrium in the 2NO 2 «2NO+O 2 system was established at concentrations =0.4 mol/l, =0.2 mol/l, =0.1 mol/l. Find the equilibrium constant and the initial concentration of NO 2 if the initial oxygen concentration is zero. What conditions will favor the shift of the equilibrium towards the formation of NO if the direct reaction is endothermic?
2. The equilibrium constant of the system A + B "C + D is equal to one. What percent of substance A will undergo a transformation if 3 moles of substance A and 5 moles of substance B are mixed? What conditions will contribute to the shift of equilibrium towards the formation of B, if the direct reaction is exothermic?
3. For system
CO (G) + H 2 O (G) "CO 2 (G) + H 2 (G)
0 = 0 =0.03 mol/l, 0 = 0 =0. Calculate the equilibrium constant if the equilibrium concentration of carbon dioxide is 0.01 mol/l. What conditions will contribute to the shift of equilibrium towards the formation of CO if the direct reaction is endothermic?
4. For system
2NO (G) + Cl 2 (G) "2NOCl (G)
0=0.5 mol/l, 0=0.2 mol/l, 0=0 mol/l. Find the equilibrium constant if by the time it occurs, 20% of nitric oxide has reacted. What conditions will favor the shift of the equilibrium towards the formation of NOCl if the direct reaction is exothermic?
H 2 (G) + I 2 (G) "2HI (G) ,
if 1 mole of iodine and 2 moles of hydrogen are placed in a vessel with a capacity of 10 liters (K C \u003d 50). What conditions will contribute to the shift of equilibrium towards the formation of iodine, if the direct reaction is exothermic?
6. For the system CO (G) + H 2 O (G) "CO 2 (G) + H 2 (G), 0 \u003d 0 \u003d 1 mol / l, 0 \u003d 0 \u003d 0. Calculate the composition of the equilibrium mixture (% vol.), if the equilibrium constant K C =1. What conditions will favor the shift of the equilibrium towards the formation of hydrogen if the reverse reaction is exothermic?
7. In a closed vessel, the reaction AB (G) “A (G) + B (G) takes place. Equilibrium constant K C =0.04. Find the initial concentration of AB if the equilibrium concentration of AB is 0.02 mol/l. What conditions will contribute to the shift of the equilibrium towards the formation of A, if the reverse reaction is exothermic?
8. In a closed vessel with a volume of 10 l at a temperature of 800˚С, an equilibrium was established CaCO 3 (T) “CaO (T) + CO 2 (G). Equilibrium constant K P =300 kPa. What mass of CaCO 3 decomposed? What conditions will contribute to the shift of equilibrium towards the formation of carbon dioxide if the direct reaction is endothermic?
9. In a closed vessel at a certain temperature, an equilibrium was established Fe (T) + H 2 O (G) “FeO (T) + H 2 (G). Determine the proportion of reacted water if K P = 1, and the initial partial pressure of hydrogen is zero. What conditions will favor the shift of the equilibrium towards the formation of hydrogen if the reverse reaction is exothermic?
10. Determine the equilibrium concentration of hydrogen in the system 2HI (G) “H 2 (G) + I 2 (G) if the initial concentration of HI was 0.05 mol / l, and the equilibrium constant K C \u003d 0.02. What conditions will contribute to the shift of equilibrium towards the formation of HI if the direct reaction is endothermic?
The rate of chemical reactions The branch of chemistry that studies the rate and mechanism of chemical reactions is called chemical kinetics. The rate of a chemical reaction is the number of elementary acts of interaction per unit of time in a unit of reaction space. This definition is valid for both homogeneous and heterogeneous processes. In the first case, the reaction space is the volume of the reaction vessel, and in the second case, the surface on which the reaction takes place. Since during the interaction the concentrations of reactants or reaction products change per unit of time. In this case, there is no need to monitor the change in the concentration of all substances participating in the reaction, since its stoichiometric equation establishes the ratio between the concentrations of the reagents. The concentration of the reactants is most often expressed as the number of moles in 1 liter (mol/l). The rate of a chemical reaction depends on the nature of the reactants, concentration, temperature, size of the contact surface of the substances, the presence of catalysts, and others. , and speak of a monomolecular reaction; when two different molecules collide in an elementary act, the dependence has the following form: u - k[A][B], and one speaks of a bimolecular reaction; when three molecules collide in an elementary act, the dependence of the velocity on concentration is true: v - k[A] [B] [C], and one speaks of a trimolecular reaction. In all analyzed dependencies: v is the reaction rate; [A], [B], [C] - concentrations of reactants; k - coefficient of proportionality; called the rate constant of the reaction. v = k when the concentrations of the reactants or their product are equal to one. The rate constant depends on the nature of the reactants and on the temperature. The dependence of the rate of simple reactions (i.e., reactions occurring through one elementary act) on concentration is described by the law of mass action established by K. Guldberg and P. Waage in 1867: the rate of a chemical reaction is directly proportional to the product of the concentration of the reacting substances raised to the power their stoichiometric coefficients. For example, for the reaction 2NO + 02 = 2N02; v - k2 and will increase three times Find: Solution: 1) Write the reaction equation: 2CO + 02 = 2CO2. According to the law of mass action, v - k[C0]2. 2) Denote [CO] = a; = b, then: v = k a2 b. 3) With an increase in the concentration of the starting substances by a factor of 3, we get: [CO] = 3a, a = 3b. 4) Calculate the reaction rate u1: - k9a23b - k27a% a if k27 D2b 27 v k a2b Answer: 27 times. Example 3 How many times will the rate of a chemical reaction increase with an increase in temperature by 40 ° C, if the temperature coefficient of the reaction rate is 3? Given: At \u003d 40 ° С Y - 3 Find: 2 Solution: 1) According to the van't Hoff rule: h-U vt2 \u003d vh y 10, 40 and, - vt\u003e 3 10 - vt -81. 2 1 1 Answer: 81 times. a Example 4 The reaction between substances A and B proceeds according to the scheme 2A + B *» C. The concentration of substance A is 10 mol / l, and substance B - b mol / l. The reaction rate constant is 0.8 l2 4 mol "2 sec"1. Calculate the rate of a chemical reaction at the initial moment, as well as at the moment when 60% of substance B remains in the reaction mixture. Given: k - 0.8 l2 mol "2 sec" 1 [A] = 10 mol / l [B] = 6 mol / l Find: "beginning! ^ Solution: 1) Find the reaction rate at the initial moment: v - k [A] 2 [B], r> \u003d 0.8 102 b - 480 mol - l sec "1. start 2) After some time, 60% of substance B will remain in the reaction mixture. Then: Therefore, [B] decreased by: 6 - 3.6 = 2.4 mol / l. 3) It follows from the reaction equation that substances A and B interact with each other in a ratio of 2: 1, therefore [A] decreased by 4.8 mol / l and became equal to: [A] \u003d 10 - 4.8 \u003d 5.2 mol/l. 4) We calculate if: d) \u003d 0.8 * 5.22 3.6 \u003d 77.9 mol l "1 * sec" 1. Answer: r>beginning ~ 480 mol l sec "1, r / \u003d 77.9 mol l-1 sec" 1. Example 5 The reaction at a temperature of 30 °C proceeds in 2 minutes. How long will it take for this reaction to end at a temperature of 60 ° C, if in a given temperature range the temperature coefficient of the reaction rate is 2? Given: t1 \u003d 30 ° С t2 \u003d 60 ° С 7 \u003d 2 t \u003d 2 min \u003d 120 sec Find: h Solution: 1) In accordance with the Van't Hoff rule: vt - \u003d y u 1 vt - \u003d 23 \u003d 8. Vt 2) The reaction rate is inversely proportional to the reaction time, therefore: Answer: t=15sec. Questions and tasks for independent solution 1. Define the reaction rate. Give examples of reactions proceeding at different rates. 2. The expression for the true rate of a chemical reaction occurring at a constant volume of the system is written as follows: dC v = ±--. d t Indicate in which cases positive and in which negative signs are needed on the right side of the expression. 3. What factors determine the rate of a chemical reaction? 4. What is called the activation energy? What factor influences the rate of a chemical reaction? 5. What explains the strong increase in the reaction rate with increasing temperature? 6. Define the basic law of chemical kinetics - the law of mass action. By whom and when was it formulated? 7. What is called the rate constant of a chemical reaction and what factors does it depend on? 8. What is a catalyst and how does it affect the rate of a chemical reaction? 9. Give examples of processes that use inhibitors. 10. What are promoters and where are they used? 11. What substances are called "catalytic poisons"? Give examples of such substances. 12. What is homogeneous and heterogeneous catalysis? Give examples of processes using their catalytic processes. 13. How will the reaction rate 2CO + 02 = 2CO2 change if the volume of the gas mixture is reduced by 2 times? 14. How many times will the rate of a chemical reaction increase with an increase in temperature from 10 ° C to 40 ° C, if it is known that with an increase in temperature by 10 ° C, the reaction rate will increase by 2 times? 15. The rate of the reaction A + B \u003d C with an increase in temperature for every 10 ° C increases three times. By how many times will the reaction rate increase when the temperature rises by 50 °C? 16. How many times will the reaction rate of the interaction of hydrogen and bromine increase if the concentrations of the starting substances are increased by 4 times? 17. How many times will the reaction rate increase with an increase in temperature by 40 ° C (y \u003d 2)? 18. How will the reaction rate 2NO + 02 ^ 2N02 change if the pressure in the system is doubled? 19. How many times should the concentration of hydrogen in the N2 + 3H2^ 2NH3 system be increased in order for the reaction rate to increase 125 times? 20. The reaction between nitric oxide (II) and chlorine proceeds according to the equation 2NO + C12 2NOC1; how the reaction rate will change with an increase in: a) the concentration of nitric oxide twice; b) chlorine concentration doubled; c) the concentration of both substances doubled? . 21. At 150°C some reaction is complete in 16 minutes. Assuming a temperature coefficient of 2.5, calculate how long it will take for the same reaction to end at 80°C. 22. By how many degrees should the temperature be increased so that the reaction rate increases by 32 times. The temperature coefficient of the reaction rate is 2. 23. At 30 ° C, the reaction proceeds in 3 minutes. How long will the same reaction take at 50 °C if the temperature coefficient of the reaction rate is 3. 24. At a temperature of 40 °C, the reaction takes 36 minutes, and at 60 °C - 4 minutes. Calculate the temperature coefficient of the reaction rate. 25. The reaction rate at 10 °C is 2 mol/l. Calculate the rate of this reaction at 50°C if the temperature coefficient of the reaction rate is 2.
Example 4.1. How will the reaction rate of each reaction change?
2NO (g) + Cl 2 (g) = 2NOCI (g) (1); CaO (c) + CO 2 (g) \u003d CaCO 3 (c) (2),
if the pressure in each system is increased by 3 times?
Solution. Reaction (1) is homogeneous and, according to the law of mass action, the initial reaction rate is v = k∙ ∙ ; reaction (2) is heterogeneous, and its rate is expressed by the equation v = k∙ . The concentration of substances in the solid phase (CaO in this reaction) does not change during the reaction, therefore it is not included in the mass action law equation.
An increase in pressure in each of the systems by 3 times will lead to a decrease in the volume of the system by 3 times and an increase in the concentration of each of the reacting gaseous substances by 3 times. At new concentrations of reaction rates: v" = k∙(3) 2 ∙3 = 27 k∙ ∙ (1) and v" = k 3 (2). Comparing the expressions for the rates v and v", we find that the rate of reaction (1) increases by 27 times, and reaction (2) by 3 times.
Example 4.2. The reaction between substances A and B is expressed by the equation 2A + B \u003d D. The initial concentrations are: C A \u003d 5 mol / l, C B \u003d 3.5 mol / l. The rate constant is 0.4. Calculate the reaction rate at the initial moment and at the moment when 60% of substance A remains in the reaction mixture.
Solution. According to the law of action of masses v = . At the initial moment, the speed v 1 \u003d 0.4 × 5 2 × 3.5 \u003d 35. After some time, 60% of substance A will remain in the reaction mixture, i.e., the concentration of substance A will become 5 × 0.6 \u003d 3 mol / l. This means that the concentration of A has decreased by 5 - 3 = 2 mol / l. Since A and B interact with each other in a ratio of 2:1, the concentration of substance B decreased by 1 mol and became equal to 3.5 - 1 = 2.5 mol / l. Therefore, v 2 \u003d 0.4 × 3 2 × 2.5 \u003d 9.
Example 4.3. Some time after the start of the reaction
2NO + O 2 \u003d 2NO 2 concentrations of substances were (mol / l): \u003d 0.06;
0.12; = 0.216. Find the initial concentrations of NO and O 2 .
Solution. The initial concentrations of NO and O 2 are found on the basis of the reaction equation, according to which 2 mol of NO is spent on the formation of 2 mol 2NO 2. According to the condition of the problem, 0.216 mol NO 2 was formed, for which 0.216 mol NO was spent. Hence, the initial concentration of NO is equal to:
0.06 + 0.216 = 0.276 mol/l.
According to the reaction equation for the formation of 2 mol NO 2, 1 mol O 2 is needed, and to obtain 0.216 mol NO 2, 0.216 / 2 = 0.108 mol / O 2 is required. The initial concentration of O 2 is: \u003d 0.12 + 0.108 \u003d 0.228 mol / l.
Thus, the initial concentrations were:
0.276 mol/l; = 0.228 mol/l.
Example 4.4. At 323 K some reaction is completed in 30 s. Determine how the reaction rate and time will change at 283 K if the temperature coefficient of the reaction rate is 2.
Solution. According to the van't Hoff rule, we find how many times the reaction rate will change:
2 –4 = .
The reaction rate decreases by 16 times. The rate of a reaction and its time are inversely related. Consequently, the time of this reaction will increase by 16 times and will be 30 × 16 = 480 s = 8 min.
Tasks
№ 4.1 . The reaction proceeds according to the equation 3Н 2 + CO = CH 4 + H 2 O
The initial concentrations of reactants were (mol/l): = 0.8; CCO = 0.6. How will the reaction rate change if the concentration of hydrogen is increased to 1.2 mol/l, and the concentration of carbon monoxide to 0.9 mol/l?
(Answer: will increase 5 times).
№ 4.2 . The decomposition reaction of N 2 O proceeds according to the equation 2N 2 O \u003d 2N 2 + O 2. The reaction rate constant is 5·10 -4 . Initial concentration
0.32 mol/l. Determine the reaction rate at the initial moment and at the moment when 50% N 2 O decomposes. ( Answer: 5,12 . 10 -5 ; 1,28 . 10 -5).
№ 4.3 . The reaction between substances A and B is expressed by the equation
A + 2B = D. Initial concentrations: C A = 0.3 mol / l and C B = 0.4 mol / l. The rate constant is 0.8. Calculate the initial rate of the reaction and determine how the reaction rate changed after some time, when the concentration of substance A decreased by 0.1 mol.
(Answer: 3,84 . 10 -2; decreased by 6 times).
№ 4.4 .What is the temperature coefficient of the reaction rate if, when the temperature drops by 30 ° C, the reaction time increases by 64 times? ( Answer: 4).
№ 4.5 .Calculate at what temperature the reaction will end in 45 minutes, if at 20 ° C it takes 3 hours. The temperature coefficient of the reaction rate is 3 ( Answer: 32.6 about C).
№ 4.6. How will the reaction rate CO + Cl 2 = COCl 2 change if the pressure is increased by 3 times and the temperature is simultaneously increased by 30 ° C (γ = 2)?
(Answer: will increase by 72 times).
№ 4.7 . The reactions proceed according to the equations
C (c) + O 2 (g) \u003d CO 2 (g) (1); 2CO (g) + O 2 (g) \u003d 2CO 2 (g) (2)
How will the rate of (1) and (2) reactions change if in each system: a) the pressure is reduced by 3 times; b) increase the volume of the vessel by 3 times; c) increase the oxygen concentration by 3 times? ( Answer: a) will decrease in (1) by 3, in (2) by 27 times);
b) will decrease in (1) by 3, in (2) by 27 times); c) will increase by (1) and (2) by 3 times).
№ 4.8 . The reaction proceeds according to the equation H 2 + I 2 \u003d 2HI. The rate constant is 0.16. The initial concentrations of hydrogen and iodine are 0.04 mol/l and 0.05 mol/l, respectively. Calculate the initial rate of the reaction and its rate when the concentration of H 2 becomes equal to 0.03 mol / l. ( Answer: 3,2 . 10 -3 ; 1,9 . 10 -3).
№ 4.9 . The oxidation of sulfur and its dioxide proceeds according to the equations:
S (k) + O 2 (g) \u003d SO 2 (g) (1); 2SO 2 (g) + O 2 (g) \u003d 2SO 3 (g) (2)
How will the rate of (1) and (2) reactions change if in each system: a) the pressure is increased by 4 times; b) reduce the volume of the vessel by 4 times; c) increase the oxygen concentration by 4 times? ( Answer: a) will increase by (1) by 4, by (2) by 64 (times);
b) will increase by (1) by 4, by (2) by 64 times); c) will increase by (1) and (2) by 4 times).
№ 4.10 . The rate constant of the reaction 2A + B = D is 0.8. Initial concentrations: C A = 2.5 mol/l and C B = 1.5 mol/l. As a result of the reaction, the concentration of substance C B turned out to be 0.6 mol / l. Calculate what became equal to C A and the rate of reaction. ( Answer: 0.7 mol/l; 0.235).
№ 4.11. The reaction proceeds according to the equation 4HCl + O 2 = 2H 2 O + 2Cl 2
Some time after the start of the reaction, the concentrations of the substances involved in it became (mol / l): \u003d 0.85; = 0.44; = 0.30. Calculate the initial concentrations of HCl and O 2 . ( Answer:= 1.45; = 0.59 mol/l).
№ 4.12 . Initial concentrations of substances in the reaction CO + H 2 O ↔ CO 2 + H 2
were equal (mol/l): C CO = 0.5; = 0.6; = 0.4; = 0.2. Calculate the concentrations of all substances involved in the reaction after 60% H 2 O has reacted. ( Answer: CCO = 0.14; = 0.24; = 0.76; = 0.56 mol/l).
№ 4.13 . How will the reaction rate 2CO + O 2 \u003d CO 2 change if:
a) increase the volume of the reaction vessel 3 times; b) increase the CO concentration by 3 times; c) increase the temperature by 40 o C (γ = 2)? ( Answer: a) will decrease by 27 times; b) will increase by 9 times; c) will increase by 16 times).
№ 4.14 . At 10°C, the reaction is complete in 20 minutes. How long will the reaction last when the temperature rises to 40 ° C, if the temperature coefficient is 3? ( Answer: 44.4 s).
№ 4.15 . How many times should be increased
a) the concentration of CO in the system 2CO \u003d CO 2 + C so that the reaction rate increases by 4 times?
b) the concentration of hydrogen in the system N 2 + 3H 2 \u003d 2NH 3 so that the reaction rate increases 100 times?
c) pressure in the system 2NO + O 2 = 2NO 2 so that the rate of formation of NO 2 increases by 10 3 times? ( Answer: 2 times; 4.64 times; 10 times).
№ 4.16 . The reaction rate A + 2B \u003d AB 2 at C A \u003d 0.15 mol / l and
C B \u003d 0.4 mol / l is equal to 2.4 ∙ 10 -3. Determine the rate constant and the reaction rate when the concentration of B becomes 0.2 mol/L. ( Answer: 0,1; 2 ∙ 10 -4).
№ 4.17 . How will the reaction rate 2A + B = A 2 B change if the concentration of substance A is increased by 3 times, the concentration of substance B is reduced by 2 times, and the temperature is increased by 40 ° C (γ \u003d 2)? ( Answer: will increase by 72 times).
№ 4.18. The reaction proceeds according to the equation 2H 2 S + 3O 2 = 2SO 2 + 2H 2 O.
Some time after the start of the reaction, the concentrations of the substances involved in it became (mol / l): \u003d 0.009; = 0.02; = 0.003. Calculate: = 0.7 mol/l).
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