Problem 325.
Find the value of the rate constant for the reaction A + B ⇒ AB, if at concentrations of substances A and B equal to 0.05 and 0.01 mol/l, respectively, the reaction rate is 5 . 10 -5 mol/(l. min).
Solution:
Speedchemical reaction expressed by the equation:

v- ,k- reaction rate constant

Answer: 0.1/mol. min.

Problem 326.
How many times will the rate of the reaction 2A + B ⇒ A 2 B change if the concentration of substance A is increased by 2 times, and the concentration of substance B is decreased by 2 times?
Solution:

v- ,k- reaction rate constant, [A] and [B] – concentrations of starting substances.

Due to an increase in the concentration of substance A by 2 times and a decrease in the concentration of substance B by 2 times, the reaction rate will be expressed by the equation:

Comparing the expressions for v and v" we find that the reaction rate has increased by 2 times.

Answer: increased by 2 times.

Problem 327.
How many times should the concentration of substance B 2 in the system be increased?
2A 2(g) + B 2(g) = 2A 2 B, so that when the concentration of substance A decreases by 4 times, the rate of the direct reaction does not change?
Solution:
The concentration of substance A was reduced by 4 times. We denote the change in the concentration of substance B by x. Then, before the concentration of substance A changes, the reaction rate can be expressed by the equation:

v- ,k- reaction rate constant, [A] and [B] – concentrations of starting substances.
After changing the concentration of substance A 2, the reaction rate will be expressed by the equation:

According to the conditions of the problem, v = v" or

Thus, it is necessary to increase the concentration of substance B 2 in the system 2A 2 (g) + B 2 (g) = 2A 2 B by 16 times, so that when the concentration of substance A 2 decreases by 4 times, the rate of the direct reaction does not change.

Answer: 16 times.

Problem 328.
Two vessels of the same capacity are introduced: into the first - 1 mole of gas A and 2 moles of gas B, into the second - 2 moles of gas A and 1 mole of gas B. The temperature in both vessels is the same. Will the reaction rate between gases A and B in these vessels differ if the reaction rate is expressed by: a) equation b) equation
Solution:
a) If the reaction rate is expressed by the equation, then, taking into account the concentrations of substances A and B in the vessels, we write down the expressions for the reaction rates for the vessels:

Thus,

b) If the reaction rate is expressed by the equation, then, taking into account the concentrations of substances A and B in the vessels, we write down the expressions for the reaction rates for the vessels:

Thus,

Answer: a) no, b) yes.

Problem 329.
Some time after the start of the reaction 3A+B ⇒ 2C+D concentrations of substances were: [A] = 0.03 mol/l; [B] =0.01 mol/l; [C] = 0.008 mol/l. What are the initial concentrations of substances A and B?

Solution:
To find the concentrations of substances A and B, we take into account that, according to the reaction equation, from 3 moles of substance A and 1 mole of substance B, 1 mole of substance C is formed. Since, according to the conditions of the problem, 0.008 moles of substance C were formed in each liter of the system, then it was consumed 0.012 moles of substance A (3/2 . 0.008 = 0.012) and 0.004 mol of substance B (1/2 . 0.008 = 0.004). Thus, the initial concentrations of substances A and B will be equal:

[A] 0 = 0.03 + 0.012 = 0.042 mol/l;
[B] 0 = 0.01 + 0.004 = 0.014 mol/l.

Answer:[A] 0 = 0.042 mol/l; [B] 0 = 0.014 mol/l.

Problem 330.
In the system CO + C1 2 = COC1 2, the concentration was increased from 0.03 to 0.12 mol/l, and the chlorine concentration from 0.02 to 0.06 mol/l. How many times did the rate of the forward reaction increase?
Solution:
Before the concentration changes, the reaction rate can be expressed by the equation:

v is the reaction rate, k is the reaction rate constant, [CO] and are the concentrations of the starting substances.

After increasing the concentration of reactants, the reaction rate is:

Let's calculate how many times the reaction rate has increased:

Answer: 12 times.

LESSON 10 10th grade(first year of study)

Fundamentals of chemical kinetics. State of chemical equilibrium Plan

1. Chemical kinetics and the field of its study.

2. Rate of homogeneous and heterogeneous reactions.

3. Dependence of the reaction rate on various factors: the nature of the reactants, the concentration of the reagents (law of mass action), temperature (van't Hoff rule), catalyst.

4. Reversible and irreversible chemical reactions.

5. Chemical equilibrium and conditions for its displacement. Le Chatelier's principle.

The branch of chemistry that studies the rates and mechanisms of chemical reactions is called chemical kinetics. One of the main concepts in this section is the concept of the rate of a chemical reaction. Some chemical reactions occur almost instantly (for example, a neutralization reaction in solution), others take thousands of years (for example, the transformation of graphite into clay during the weathering of rocks).

Speed homogeneous reaction is the amount of a substance that reacts or is formed as a result of a reaction per unit time per unit volume of the system:

In other words, the rate of a homogeneous reaction is equal to the change in the molar concentration of any of the reactants per unit time. The reaction rate is a positive quantity, therefore, when expressing it through a change in the concentration of the reaction product, a “+” sign is given, and when the reagent concentration changes, a “–” sign is given.

The rate of a heterogeneous reaction is the amount of substance that reacts or is formed as a result of a reaction per unit time per unit surface area of ​​the phase:

The most important factors influencing the rate of a chemical reaction are the nature and concentration of the reagents, temperature, and the presence of a catalyst.

Influence nature of the reagents manifests itself in the fact that, under the same conditions, different substances interact with each other at different rates, for example:

When increasing reagent concentrations the number of collisions between particles increases, which leads to an increase in the reaction rate. The quantitative dependence of the reaction rate on the concentration of reagents is expressed by the law of effective mass (K.M. Guldberg and P. Waage, 1867; N.I. Beketov , 1865). The rate of a homogeneous chemical reaction at a constant temperature is directly proportional to the product of the concentration of the reacting substances in powers equal to their stoichiometric coefficients (concentration solids are not taken into account), for example:

where A and B are gases or liquids, k – reaction rate constant equal to the reaction rate at a reactant concentration of 1 mol/l. Constant k depends on the properties of the reacting substances and temperature, but does not depend on the concentration of the substances.

Dependence of reaction speed on temperature is described by the experimental rule of Van t-Goff (1884). When the temperature increases by 10°, the rate of most chemical reactions increases by 2–4 times:

where is the temperature coefficient.

Catalyst is a substance that changes the rate of a chemical reaction, but is not consumed as a result of this reaction. There are positive catalysts (specific and universal), negative (inhibitors) and biological (enzymes, or enzymes). The change in reaction rate in the presence of catalysts is called catalysis. There are homogeneous and heterogeneous catalysis. If the reactants and the catalyst are in the same state of aggregation, catalysis is homogeneous; in different – ​​heterogeneous.

Homogeneous catalysis:

heterogeneous catalysis:

The mechanism of action of catalysts is very complex and not fully understood. There is a hypothesis about the formation of intermediate compounds between the reagent and the catalyst:

A + cat. ,

B AB + cat.

Promoters are used to enhance the action of catalysts; There are also catalytic poisons that weaken the effect of catalysts.

The rate of a heterogeneous reaction is affected by interfacial area(the degree of grinding of the substance) and the rate of supply of reagents and removal of reaction products from the phase interface.

All chemical reactions are divided into two types: reversible and irreversible.

Chemical reactions that proceed in only one direction are called irreversible., i.e. the products of these reactions do not interact with each other to form the starting materials. Conditions for the irreversibility of a reaction are the formation of a precipitate, gas or weak electrolyte. For example:

BaCl 2 + H 2 SO 4 = BaSO 4 + 2HCl,

K 2 S + 2HCl = 2KCl + H 2 S,

HCl + NaOH = NaCl + H 2 O.

Reversible reactions are those that occur simultaneously in the forward and reverse directions., For example:

When a reversible chemical reaction occurs, the rate of the direct reaction initially has a maximum value, and then decreases due to a decrease in the concentration of the starting substances. The reverse reaction, on the contrary, at the initial moment of time has a minimum speed, which gradually increases. Thus, at a certain point in time there comes state chemical equilibrium , at which the rate of the forward reaction is equal to the rate of the reverse reaction. The state of chemical equilibrium is dynamic - both forward and reverse reactions continue to occur, but since their rates are equal, the concentrations of all substances in the reaction system do not change. These concentrations are called equilibrium.

The ratio of the rate constants of forward and reverse reactions is a constant value and is called the equilibrium constant ( TO R ) . Solid concentrations are not included in the equilibrium constant expression. The equilibrium constant of the reaction depends on temperature and pressure, but does not depend on the concentration of the reactants and on the presence of a catalyst, which accelerates the progress of both forward and reverse reactions. The more TO p, the higher practical solution reaction products. If TO p > 1, then the reaction products predominate in the system; If TO R< 1, в системе преобладают реагенты.

Chemical equilibrium is mobile, i.e. when external conditions change, the speed of the forward or reverse reaction may increase. The direction of the equilibrium shift is determined by the principle formulated by the French scientist Le Chatelier in 1884. If an external influence is exerted on an equilibrium system, then the equilibrium shifts towards the reaction that counteracts this influence. Equilibrium shifts are affected by changes in reactant concentrations, temperature, and pressure.

An increase in the concentration of reagents and the removal of products lead to a shift in equilibrium towards the direct reaction.

When the system is heated, the equilibrium shifts towards the endothermic reaction, and when cooled, towards the exothermic reaction.

For reactions involving gaseous substances, an increase in pressure shifts the equilibrium towards a reaction that occurs with a decrease in the number of gas molecules. If the reaction proceeds without changing the number of molecules of gaseous substances, then the change in pressure does not in any way affect the shift in equilibrium.

1. In a vessel, gas A with an amount of substance of 4.5 mol and gas B with an amount of substance of 3 mol were mixed. Gases A and B react in accordance with the equation A + B = C. After some time, gas C was formed in the system with an amount of substance of 2 mol. What quantities of unreacted gases A and B remain in the system?

From the reaction equation it follows that:

Dn(A) = Dn(B) = Dn(C) = 2 mol,

where Dn is the change in the amount of substance during the reaction.

Therefore, what remains in the vessel is:

n 2 (A) = n 1 (A) - Dn(A); n 2 (A) = (4.5 - 2) mol = 2.5 mol;

n 2 (B) = n 1 (B) - Dn(B); n 2 (B) = (3 - 2) mol = 1 mol.

2. The reaction proceeds according to the equation: 2A + B ⇄ C and is second order in substance A and first order in 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 forward reaction at the moment when 50% of substance B reacts if the initial concentrations are: C(A) = 10 mol/l; C(B) = 5 mol/l. How will the rate of a chemical reaction change?

C(B) that entered into the reaction is equal to:

C(B) = 0.5 5 = 2.5 mol/l.

Accordingly, C(A) that 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) = 10 - 5 = 5 mol/l,

C(B) = 5 - 2.5 = 2.5 mol/l.

The rate of the forward reaction will be equal to:

The rate of the 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 = C and has the first order for substance A and the second for substance B. The initial concentrations of the substances are: C(A) = 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 decreases by 0.3 × 2 = 0.6 mol/l. After the reaction occurs, the concentrations are:

4. The rates of forward 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 forward and reverse reactions under initial conditions are equal:

An increase in pressure by 3 times for gaseous systems leads to a decrease in the volume of the gas mixture by 3 times, the concentrations of all three gases will increase by the same amount, and the rates of both reactions will become correspondingly equal:

The reaction rate ratios are:

Thus, the rate of the forward reaction will increase by 27 times, the reverse reaction by 9.

5. The reaction at a temperature of 50 0 C proceeds in 2 minutes 15 s. How long will it take for this reaction to complete at a temperature of 70 0 C, if in this temperature range the temperature coefficient of rate g is 3?

As the temperature increases from 50 to 70 0 C, the reaction rate increases in accordance with the Van't Hoff rule:

Where = 70 0 C, = 50 0 C, a and are the reaction rates at given temperatures.

We get:

those. the reaction rate increases 9 times.

According to the definition, reaction time is inversely proportional to the rate of reaction, therefore:

where and is the reaction time at temperatures And .

From here we get:

Considering that = 135 s (2 min 15 s), we determine the reaction time at temperature :

6. How many times will the rate of a chemical reaction increase when the temperature increases from = 10 0 C to = 80 0 C , if the temperature coefficient of speed g is 2?

From van't Hoff's rule:

The reaction speed will increase 128 times.

7. When studying the kinetics of drug elimination from the patient’s body, it was found that after 3 hours, 50% of the original amount of the drug remained in the patient’s body. Determine the half-life and rate constant for the reaction of drug removal from the human body, if it is known that this is a first-order reaction.

Since during a given period of time 50% of the drug was removed from the body, then t 1/2 = 3 hours. Let's calculate the reaction rate constant from the equation:

8. During laboratory tests aqueous solutions of the drug, it was found that due to hydrolysis, the concentration of the drug decreased from 0.05 mol/l to 0.03 mol/l per day. Calculate the half-life of the drug hydrolysis reaction.

Since hydrolysis reactions usually occur with a significant excess of water, its concentration can be kept constant. Consequently, during the reaction only the concentration of the drug changes 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 eliminated from the body.

When 75% of the drug is excreted 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 for the reaction of sucrose hydrolysis is 2.31×10 - 3 h - 1. Calculate:

1) half-life of the reaction;

2) the time during which 20% of sucrose will undergo hydrolysis;

3) what part of glucose will undergo hydrolysis after 5 days.

1. The half-life is equal to:

2. After 20% of sucrose has undergone hydrolysis, the C/C 0 ratio will be 0.8. Hence:

3. After 5 days (120 hours), the C/C 0 ratio will be:

Consequently, 24% of glucose was hydrolyzed.

11. During a certain first-order reaction, 60% of the initial amount of a substance undergoes transformation in 30 minutes. Determine what part of the substance will remain after 1 hour.

1. After 30 minutes, the amount of remaining substance will be:

C 1 = C 0 - 0.6 C 0 = 0.4 × C 0.

i.e., the ratio C 0 /C 1 is 2.5.

2. Let's find the reaction rate constant:

3. The amount of substance C2 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 the rate of a chemical reaction called?

2. What is the true rate of a homogeneous reaction?

3. What is the dimension of the rate of a homogeneous reaction?

4. What is the rate of a heterogeneous reaction called?

5. What is the dimension of the rate of a heterogeneous reaction?

6. List the factors influencing the speed of the reaction.

7. Formulate the law of mass action.

8. What is physical meaning reaction rate constants? What does the reaction rate constant depend on and what does it not depend on?

9. What is the order of reaction? 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 a reaction?

13. Define simple and complex reactions. Give a classification of complex reactions.

14. Formulate Van't Hoff's rule. Bring mathematical expression van't Hoff's rules.

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 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 #1

1. The reaction between substances A and B is expressed by the equation 2A + B = C and is second order for substance A and first order for substance B. The initial concentrations of substances are: C 0 (A) = 0.4 mol/l; C 0 (B) = 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. How many degrees must the temperature be increased for the reaction rate to increase 64 times? The temperature coefficient of the reaction rate g is equal to 2.

a) when the pressure in the system doubles?

b) when the volume of gases doubles?

Option No. 2

1. The reaction proceeds according to the equation: A + B = C and is of 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. How many times 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 later the reaction would end 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 increases by 3 times?

Option #3

1. The reaction is expressed by the equation: A + B = C and has first order in substance A and substance B. At initial concentrations C 0 (A) = 3 mol/l and C 0 (B) = 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 when the temperature increases from 10 to 70 0 C, if the temperature coefficient of the rate g is 2?

3. The reaction rate A (s) + 2B (gas) = ​​C (s) is expressed by the equation: How will the reaction rate change if the concentration of B is doubled?

Option No. 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 for it to end at 80 0 C if the temperature coefficient of speed g is 3?

3. The rate of reaction 3A + B = C is expressed by the equation: How many times will the rate of the forward reaction change:

a) when the concentration of substance A doubles?

b) with a simultaneous decrease in the concentration of the starting substances by 2 times?

Option #5

1. The rate of a certain reaction increased 8 times when the temperature increased from 40 to 70 0 C. Determine the value of g.

2. The reaction proceeds according to the equation: A + 3B = 2C and is of first order in substance A and second in 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 forward and reverse reactions occurring in the gas phase and obeying the equations change:

Option #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 forward reaction is described by the equation How many times will the rate of the forward reaction decrease after 0.5 mol of A reacts?

2. By how many degrees must the temperature be increased for the reaction rate to increase 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 No. 7

1. The reaction between substances A and B proceeds according to the equation: A + 2B = C and is of first order in substance A and substance B. The initial concentrations of the reacting substances were: C 0 (A) = 1.5 mol/l; C 0 (B) = 3 mol/l; k = 0.4. Calculate the rate of the chemical reaction at the initial moment of time and after some time, when 75% of A has reacted.

2. What is the temperature coefficient of rate g, if with an increase in temperature by 30 0 C, the reaction rate increases 27 times?

3. How will the rates of forward and reverse reactions occurring in the gas phase and obeying the equations change:

with an isothermal increase in pressure by a factor of 2?

Option No. 8

1. In a 1 liter solution containing 1 mol of substance A and 2 mol of substance B, the following reaction occurs: A + 3B = 2C + D. The direct reaction is first order in substance A and second order in substance B. How many times will the rate of the direct reaction decrease? reaction after 0.65 mol of substance A has reacted?

2. When the temperature increases from -5 to +5 0 C, the rate of bacterial hydrolysis (enzymatic process) increases 4 times. Find the value of the temperature coefficient of the reaction rate g.

3. How many times should the concentration of substance A in the system 2A (gas) = ​​B (gas) + C (solid) be increased so that the rate of the direct reaction, which is a second-order reaction, increases 4 times?

Option No. 9

1. The reaction proceeds according to the equation: 2A + B = 2C and is second order in substance A and first order in 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) = 1 mol/l. How will the rate of a chemical reaction change?

2. When the temperature increased from 10 to 50 0 C, the reaction rate increased 16 times. Determine the temperature coefficient of speed g.

3. The reaction proceeds according to the equation: A + B = C + D + E and has first order in substance A and zero in substance B. How will the rate of the direct reaction change after diluting the reacting mixture by 3 times?

Option No. 10

1. The reaction proceeds according to the equation: A + 2B = AB 2 and is first order in substance A and 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) = 0.8 mol/l and the reaction rate at the time of formation of 0.2 mol/l substance AB 2.

2. How many times will the rate of a chemical reaction increase when the temperature increases 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 how long it will take to reduce the content of the drug in the human body by 8 times.

Option No. 11

1. The reaction proceeds according to the equation: A + B = 2C and is of first order in substance A and substance B. The initial concentrations of substances are: C 0 (A) = 0.3 mol/l; C 0 (B) = 0.5 mol/l; k = 0.1. Find the initial reaction rate and the reaction rate after some time, when the concentration of A decreases by 0.1 mol/l.

2. At 100 0 C, some reaction ends in 16 minutes. Taking the temperature coefficient of rate g equal to 2, calculate how many minutes later would the same reaction end 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 eliminated from the body.

Option No. 12

1. The reaction proceeds according to the equation: A + 2B = C and is of first order in substance A and second in substance B. The initial concentrations of substances are: C 0 (A) = 0.9 mol/l; C 0 (B) = 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 is consumed.

2. What is the temperature coefficient of the rate of a chemical reaction g? , if with an increase in temperature by 30 0 C the speed increases by 27 times?

3. The half-life of a certain first-order reaction is 30 minutes. Calculate what portion of the original amount will remain after 1 hour.

Option No. 13

1. The reaction proceeds according to the equation: 2A + B = 2C and is second order in substance A and first order in 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) = 0.9 mol/l and the reaction rate at the time of formation of 0.1 mol of substance C.

2. At a temperature of 10 0 C, the reaction takes place in 80 minutes. At what temperature will the reaction complete in 20 minutes if the temperature coefficient of rate g is 2?

3. During laboratory research it was found that within 24 hours 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 is a first-order reaction.

Option No. 14

1. In a closed vessel with a volume of 1 liter 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 forward reaction is first order with respect to substance A and second order with respect to substance B. How will the rate of the forward reaction change after 0.5 mol of gas A reacts?

2. When the temperature of the system increased from 10 to 50 0 C, the rate of the chemical reaction increased 16 times. Determine the temperature coefficient of the reaction rate g .

3. During an accident Chernobyl nuclear power plant(1986) there was a release of the radionuclide Cs-137, the half-life of which is 30 years. Calculate what part of the radionuclide that entered the body remains at the present time.

Option No. 15

1. The reaction proceeds according to the equation: A + B = C has the first order in substance A and in substance B. At the initial concentrations of substances C 0 (A) = 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 for 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 how long it will take for the pesticide concentration to decrease to 0.01 mol/l.

Option No. 16

1. The decomposition reaction proceeds according to the equation: 2A = 2B + C and is of second order in substance A. The rate constant of this reaction at 200 0 C is 0.05. Initial concentration C(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 (solid) + 3B (gas) = ​​2C (solv), which has zero order in substance A and third order in substance B, if the pressure in the system is increased by 3 times?

3. During a certain 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 No. 17

1. The interaction of gases proceeds according to the equation: A + 2B = 2C and is of the first order in substance A and second in substance B. The initial concentrations of gases are equal to: 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 time and after some time, when 50% of substance A has reacted.

2. At 20 0 C the reaction occurs in 2 minutes. How long will it take for the same reaction to occur 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 equal to 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 No. 18

1. The reaction proceeds according to the equation: 2A + B = 2C and is of first order in substance A and substance B. The reaction rate is 0.5 mol/l×s. The initial concentrations of substances are: C(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 occurs in 2 minutes. How long will it take for the same reaction to occur at 50 0 C if g = 2?

3. The rate constant for the inversion reaction of cane sugar at 25 0 C is equal to 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.

Irreversible reactions

1. How will the rate of reaction 2A + B ® A 2 B change if the concentration of substance A is increased by 2 times, and the concentration of substance B is decreased by 2 times?

2. How many times should the concentration of substance B 2 in the system 2A 2 (g) + B 2 (g) ® 2A 2 B (g) be increased 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 ® COC1 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. How many times 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 when a) the CO concentration increases by 2 times; b) concentration of C1 2 2 times; c) the concentrations of both substances are 2 times?

7. The reaction takes place in the gas phase. The reaction involves two substances A and B. It is known that when the concentration of component A is doubled, the rate increases 2 times, and when the concentration of component B doubles, the rate increases 4 times. Write an equation for the reaction that occurs. How will the reaction rate change when the total pressure increases by 3 times?

8. The reaction rate of the interaction of substances A, B and D is studied. At constant concentrations of 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 reaction rate when the pressure increases by 3 times.

10. Find the value of the rate constant for the reaction A + 2B ® AB 2, if at the 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 liters, gas A with an amount of substance of 4.5 mol and gas B with an amount of substance of 3 mol were mixed. Gases react in accordance with the equation A + B = C. After 20 seconds, gas C was formed in the system with an amount of substance of 2 mol. Define average speed reactions. What quantities 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 resulting substance C becomes equal to 0.01 mol/l.

13. Reaction between gaseous substances A and B are 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 so that the rate of a chemical reaction becomes equal to the original rate?

14. How many degrees must the temperature be increased for the reaction rate to increase 27 times? The temperature coefficient of the reaction rate is 3.

15. At 20 o C the reaction proceeds in 2 minutes. How long will this reaction take to occur 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 takes place 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 o C if the temperature coefficient of rate is 3.

18. With an increase in temperature by 50 o C, the reaction rate increased 32 times. Calculate the temperature coefficient of the rate of a chemical reaction.

19. Two reactions occur at 25 o C at the same rate. The temperature coefficient of the rate of the first reaction is 2.0, and the second is 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, with an increase in temperature from 290 to 300 K, the reaction rate increases by 2 times?

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 when the temperature increases from 27 to 37 o 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 effective? Justify the answer by calculating the ratio of reaction rates when using a particular catalyst.

25. At 150 o C, some reaction ends in 16 minutes. Taking the temperature coefficient of the reaction rate equal to 2.5, calculate the time after which this reaction will end if it is carried out a) at 200 o C, b) at 80 o C.

26. When the temperature increases by 10 o C, the rate of a chemical reaction doubles. At 20 o C 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 o C, the rate of the chemical reaction is 0.04 mol/(l×s). Calculate the rate of this reaction at 70 o C, if it is known that the activation energy is 70 kJ/mol.

28. Calculate the temperature coefficient of the reaction g, if the rate constant of this reaction at 120 o C is equal to 5.88 × 10 -4, and at 170 o C - 6.7 × 10 -2.

29. How many times will the rate of a chemical reaction change when the temperature increases 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 when the pressure in the system increases by 4 times and the temperature simultaneously increases by 40 o C. The reactants 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 decreases by 3 times and the temperature of the system simultaneously decreases 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 the 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 o C?

33. It is known that when the temperature increases 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, 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 promote a shift in 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 unity. What percentage of substance A will be converted if you mix 3 moles of substance A and 5 moles of substance B? What conditions will contribute to a shift in equilibrium towards the formation of B if the direct reaction is exothermic?

3. For the 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 carbon dioxide equal to 0.01 mol/l. What conditions will contribute to a shift in equilibrium towards the formation of CO if the direct reaction is endothermic?

4. For the 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 of its onset 20% of nitric oxide has reacted. What conditions will contribute to a shift in 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 (KC = 50). What conditions will contribute to a shift in 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 = 0 =1 mol/l, 0 = 0 =0. Calculate the composition of the equilibrium mixture (% vol.), if the equilibrium constant K C = 1. What conditions will contribute to a shift in 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 a shift in equilibrium towards the formation of A if the reverse reaction is exothermic?

8. In a closed vessel with a volume of 10 liters at a temperature of 800˚C, the equilibrium CaCO 3 (T) “CaO (T) + CO 2 (G) has been established. Equilibrium constant K P =300 kPa. What mass of CaCO 3 decomposed? What conditions will contribute to a shift in equilibrium towards the formation of carbon dioxide if the direct reaction is endothermic?

9. In a closed vessel at a certain temperature, the equilibrium Fe (T) + H 2 O (G) “FeO (T) + H 2 (G) has been established. Determine the fraction of reacted water if K P = 1 and the initial partial pressure of hydrogen is zero. What conditions will contribute to a shift in 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 = 0.02. What conditions will contribute to a shift in equilibrium towards the formation of HI if the direct reaction is endothermic?

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, the surface on which the reaction occurs. Since the interaction changes the concentrations of reagents or reaction products per unit time. In this case, there is no need to monitor changes in the concentration of all substances participating in the reaction, since its stoichiometric equation establishes the relationship between the concentrations of the reactants. The concentration of 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 reacting substances, concentration, temperature, size of the contact surface of the substances, the presence of catalysts and others. , and talk about a monomolecular reaction; when a collision of two different molecules occurs in an elementary act, the dependence has the following form: u - k[A][B], and they speak of a bimolecular reaction; when a collision of three molecules occurs in an elementary act, the dependence of speed on concentration is true: v - k [A] [B] [C], and they speak of a trimolecular reaction. In all analyzed dependencies: v - reaction rate; [A], [B], [C] - concentrations of reacting substances; k - proportionality coefficient; called the reaction rate constant. v = k, when the concentrations of reactants or their product are equal to unity. 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: 2СО + 02 = 2С02. According to the law of mass action v - k[C0]2. 2) Let us denote [CO] = a; = b, then: v = k a2 b. 3) When the concentration of the starting substances increases by 3 times, we obtain: [CO] = 3a, a = 3b. 4) Calculate the speed of reaction 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 when the temperature increases by 40 °C if the temperature coefficient of the reaction rate is 3? Given: At = 40 °C Y - 3 Find: 2 Solution: 1) According to Van't Hoff's rule: h-U vt2 = vh y 10, 40 and, - vt > 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 is 6 mol/l. The reaction rate constant is 0.8 l2 4 mol"2 sec"1. Calculate the rate of the 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: "start! ^ Solution: 1) Find the reaction rate at the initial moment: v - k[A]2 [B], r> = 0.8 102 b - 480 mol - l sec"1. beginning 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) From the reaction equation it follows 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] = 10 - 4.8 = 5.2 mol/l. 4) Calculate if: d) = 0.8 * 5.22 3.6 = 77.9 mol l "1 * sec"1. Answer: g>begin ~ 480 mol l sec"1, g/ = 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 complete at a temperature of 60 °C, if in this temperature range the temperature coefficient of the reaction rate is 2? Given: t1 = 30 °C t2 = 60 °C 7 = 2 t = 2 min = 120 sec Find: h Solution: 1) In accordance with the van’t Hoff rule: vt - = y 1 vt - = 23 = 8. Vt 2) The reaction speed is inversely proportional to the reaction time, therefore: Answer: t = 15 sec. Questions and tasks for independent solution 1. Define reaction rate. Give examples of reactions occurring 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 a positive and in which a negative sign is needed on the right side of the expression. 3. On what factors does the rate of a chemical reaction depend? 4. What is called activation energy? What factor influences the rate of a chemical reaction does it characterize? 5. What explains the strong increase in reaction rate with increasing temperature? 6. Define the basic law of chemical kinetics - the law of mass action. Who and when was it formulated? 7. What is the rate constant of a chemical reaction called 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 in which inhibitors are used. 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 2С0 + 02 = 2С02 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 when the temperature increases 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 reaction A + B = C increases three times with every 10 °C increase in temperature. How many times will the reaction rate increase when the temperature increases by 50 °C? 16. How many times will the rate of the reaction between 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 when the temperature increases by 40 °C (y = 2)? 18. How will the rate of the reaction 2NO + 02 ^ 2N02 change if the pressure in the system is doubled? 19. How many times should the concentration of hydrogen in the system N2 + 3H2^2NH3 be increased so that the reaction rate increases by 125 times? 20. The reaction between nitrogen oxide (II) and chlorine proceeds according to the equation 2NO + C12 2NOC1; How will the reaction rate change when: a) the concentration of nitric oxide doubles; b) chlorine concentration doubled; c) the concentrations of both substances are doubled? . 21. At 150 °C, some reaction ends in 16 minutes. Taking the temperature coefficient equal to 2.5, calculate the time period after which the same reaction will end at 80 °C. 22. How many degrees must the temperature be increased for the reaction rate to increase 32 times? The temperature coefficient of the reaction rate is 2. 23. At 30 °C, the reaction occurs in 3 minutes. How long will it take for the same reaction to occur at 50 °C if the temperature coefficient of the reaction rate is 3. 24. At a temperature of 40 °C the reaction proceeds in 36 minutes, and at 60 °C in 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.