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How to change the concentration of substances. Let's consider how a change in temperature affects the equilibrium

In accordance with Le Chatelier's principle, heating causes a shift in equilibrium towards which of two opposing processes, the occurrence of which is accompanied by the absorption of heat. Means an increase in temperature causes an increase in the equilibrium constant of the endothermic process. Naturally, a decrease in temperature leads to a shift in equilibrium towards that process, the occurrence of which is accompanied by the release of heat . Cooling favors the exothermic process and causes an increase in its equilibrium constant.

Changes in pressure also affect balance.

At constant temperature, the equilibrium constant does not change under the influence of pressure. However, the relative amounts of starting substances and products under the influence of pressure change in the direction predicted by Le Chatelier's principle. If you increase the pressure at a constant temperature, the volume of the gas mixture decreases and the concentration of the reactants increases. In this case, the increase in pressure will be compensated by the fact that the reaction will proceed in the direction corresponding to a decrease in the total number of moles of gases present (in the direction of decreasing concentration). As the pressure decreases, the equilibrium will shift towards the reaction with a large number moles.

Equilibrium is also affected by changes in concentration.

In accordance with Le Chatelier's principle, the introduction of additional quantities of a reagent into an equilibrium system causes a shift in the equilibrium in the direction in which its concentration decreases. Therefore, an excess of the starting substance(s) causes the equilibrium to shift to the right. The addition of the reaction product(s) causes the equilibrium to shift to the left.

EXAMPLES OF SOLVING PROBLEMS

Task 1. Given the system

N 2(g) + 3H 2(g) 2NH 3(g); ΔH<0.

a) increase the pressure in the system; b) lower the temperature; c) increase the concentration of hydrogen.

Solution: In accordance with the law of mass action, we write down the expressions for the rate of direct reaction:

;

The system is homogeneous, all substances are in a gaseous state. When the volume of the system is reduced by 2 times, the concentration of reagents also increases by 2 times. Let's write down new expressions for reaction rates:

Therefore, the rate of the forward reaction will increase by

The equilibrium constant of this reaction will be written as follows:

If the pressure in the system is increased, the volume will decrease and the concentration of reagents will increase. Consequently, the equilibrium will shift towards the reaction that reduces the concentration. Since in this reaction there are 4 moles of substance on the left side of the equation, and 2 moles on the right side, the equilibrium will shift to the right.

The reaction is exothermic, that is, it releases heat. If we lower the temperature, the equilibrium will shift to the right, towards the exothermic reaction.

As the hydrogen concentration increases, the equilibrium will shift towards the reaction that reduces the hydrogen concentration, in this case to the right.

Task 2.

In the reaction C(t)+2H 2 (g) CH 4 (g), the hydrogen concentration was reduced by 3 times. How will the reaction rate change?

Solution.

According to the law of mass action, the initial reaction rate is v n =k× 2. After reducing the hydrogen concentration by 3 times, the speed will become equal to v к =k×(1/3) 2 2 =1/9k 2. . After changing the hydrogen concentration, the speed will change as follows: v k /v n =1/9k 2 /k 2 =1/9. Answer: the reaction rate will decrease by 9 times.

Task 3.

In which direction will the equilibrium of the reaction 2SO 2 (g) + O 2 (g) 2SO 3 (g) shift? DH°<0 при повышении температуры?

Solution.

Since DH°<0, теплота выделяется в ходе прямой реакции, которая является экзотермической. Обратная реакция будет эндотермической. Повышение температуры всегда способствует протеканию реакции с поглощением теплоты, т.е. равновесие сместится в сторону исходных веществ.

Answer: left.

Task 4. How will the reaction rate change when the temperature increases from 20 0 C to 60 0 C if the temperature coefficient of the reaction rate is 2?

Solution: To solve, we apply the Van't Hoff rule:

; .

Consequently, the reaction rate with increasing temperature will increase 16 times.

Task 5. At a temperature of 50 0 C, some reaction ends in 2 minutes. 15 s. Taking the temperature coefficient of the reaction rate equal to 2, calculate how long it will take for this reaction to end if it is carried out at 70 0 C?

Solution: Using van't Hoff's rule, we calculate how many times the reaction rate will change.

; h begins attitude: .

The speed of the reaction is inversely proportional to the reaction time. Therefore, we can write:

From here we find: .

The reaction will end in 15 seconds.

CONTROL QUESTIONS

In problems Nos. 31-45 the equations of reactions that are in a state of equilibrium are given. Solve the problem according to the condition.

Problem 31

2H 2 (g) + O 2 (g) 2H 2 O (g); ; ∆Н°

1. How will the rate of the direct reaction change if the pressure in the system is doubled?

2. How many times will the reaction rate change if the temperature is increased by 50 0 C? γ = 2.

Problem 32

A (t) + 2B (g) C (t); ∆Н°

2. How many times will the reaction rate change if the temperature is increased by 20 0 C? γ = 2.

Problem 33

CO 2 (g) + H 2 (g) CO (g) + H 2 O (g) , ∆Н°

1. How will the rate of the direct reaction change if the concentration of hydrogen is increased by 3 times?

2. How many times will the reaction rate change if the temperature is lowered by 30 0 C? γ = 4.

a) increase the temperature;

b) lower the pressure?

Problem 34

A 2(g) + 3B (g) 2C (t) + 4D (g); ∆Н°

1. How will the rate of the reverse reaction change if the volume of the system is reduced by 2 times?

2. How many times will the reaction rate change if the temperature is lowered by 20 0 C? γ = 3.

Problem 35

2SO 2 (g) + O 2 (g) 2SO 3 (g); ∆Н°

1. How will the rate of the direct reaction change if the concentration of SO 2 is increased by 2 times and the concentration of O 2 is decreased by 2 times?

2. How many times will the reaction rate change if the temperature is increased by 30 0 C? γ = 2.

3. Write an expression for the equilibrium constant. Where will the equilibrium shift if:

a) lower the temperature;

b) increase the pressure?

Problem 36

N 2 (g) + 3H 2 (g) 2NH 3 (g); ∆H 0< 0

1. How will the rate of the direct reaction change if the pressure in the system is reduced by 3 times?

2. What is the temperature coefficient if the temperature was lowered by 40 0 C and the reaction rate changed 81 times?

3. Write an expression for the equilibrium constant. Where will the equilibrium shift if

a) increase the concentration of N 2;

b) reduce the temperature?

Problem 37

FeO(s) + CO(g) Fe(s) + CO 2 (g); ∆H 0 > 0

1. How will the rate of the forward reaction change if the CO concentration is increased 5 times?

2. How many times will the reaction rate change if the temperature is increased by 10 0 C? γ = 3.

3. Write an expression for the equilibrium constant. How should the volume and temperature be changed to shift the equilibrium to the left?

Problem 38

MgCO 3 (t) MgO (t) + CO 2 (g); ∆H 0< 0

1. How will the rate of the reverse reaction change if the volume of CO 2 is increased by 3 times?

2. What is the temperature coefficient of the reaction if the reaction rate changes 8 times when the temperature decreases by 30 0 C?

3. Write an expression for the equilibrium constant. Where will the equilibrium shift as the temperature decreases and the CO 2 concentration decreases?

Problem 39

2N 2 O(g) 2N 2 (g) + O 2 (g); ∆H 0< 0

2. How many times will the reaction rate change if the temperature is increased by 40 0 C? γ = 3

3. Write an expression for the equilibrium constant. Where will the equilibrium shift as temperature and pressure decrease?

Problem 40

4HCl(g) + O 2 (g) 2H 2 O(g) + 2Cl 2 ; ∆H 0< 0

1. How will the rate of the direct reaction change if the concentration of HCl is reduced by 2 times and the concentration of O 2 is increased by 8 times?

2. How many times will the reaction rate change if the temperature is lowered by 50 0 C? γ = 2

3. Write an expression for the equilibrium constant. How should the pressure and temperature be changed to shift the equilibrium to the left?

Problem 41

N 2 O 4 (g) 2NO 2 (g); ∆H 0 > 0

1. How will the rate of the reverse reaction change if the pressure is increased by 4 times?

2. What is the temperature coefficient of the reaction if the reaction rate changes by 2 times when the temperature decreases by 10 0 C?

3. Write an expression for the equilibrium constant. How should the pressure and temperature be changed to shift the equilibrium to the left?

Problem 42

2AB(g) A 2 (g) + 2B(g) ; ∆H 0 > 0

1. How will the rate of the reverse reaction change if the concentration of A 2 is reduced by 5 times?

2. How many degrees should the temperature be increased if the reaction rate has changed 8 times?γ =2

3. Write an expression for the equilibrium constant. How should the pressure and temperature be changed to shift the equilibrium to the right?

Problem 43

C(t) + CO 2 (g) 2CO(g); ∆H 0 > 0

1. How will the rate of the direct reaction change if the volume is reduced by 10 times?

2. How many degrees must the temperature be lowered for the reaction rate to change 16 times? γ = 2.

3. Write an expression for the equilibrium constant. Where will the equilibrium shift if the pressure and temperature are increased?

Problem 44

2CO (g) + O 2 (g) 2CO 2 (g); ∆H 0 ‹ 0

1. How will the rate of the direct reaction change if the pressure is increased 5 times?

2. How many degrees must the temperature be increased for the reaction rate to increase 64 times? γ = 2.

3. Write an expression for the equilibrium constant. How should the volume and temperature be changed to shift the equilibrium to the left?

Problem 45

N 2 (g) + O 2 (g) 2NO (g); ∆H 0 › 0

1. How will the rate of the reverse reaction change if the volume is reduced by 3 times?

2. How many degrees must the temperature be lowered for the reaction rate to decrease by 27 times? γ = 3

3. Write an expression for the equilibrium constant. How should the pressure and temperature be changed to shift the equilibrium to the right?

Problem 46

CaCO 3 (k) CaO (k) + CO 2 (g); ∆H 0 › 0

1. How will the rate of the reverse reaction change if the concentration of CO 2 is increased 7 times?

2. How many degrees must the temperature be increased to increase the reaction rate by 27 times? γ =3

3. Write an expression for the equilibrium constant. Where will the equilibrium shift if:

a) lower the temperature:

b) increase the pressure?

Problem 47

2NO(g) + O 2 (g) 2NO 2 (g); ∆H 0 ‹ 0

1. How will the rate of the direct reaction change if the volume is reduced by 3 times?

2. How many degrees must the temperature be lowered for the reaction rate to decrease by 64 times? γ = 3

3. Write an expression for the equilibrium constant. How should the temperature and concentration of NO be changed to shift the equilibrium to the right?

Problem 48

COCl 2 (g) CO (g) + Cl 2 (g); ∆H 0 › 0

1. How will the rate of the reverse reaction change if the CO concentration is increased by 4 times and the Cl 2 concentration is reduced by 2 times?

2. How many degrees must the temperature be increased to increase the reaction rate by 9 times? γ = 3.

3. Write an expression for the equilibrium constant. Where will the equilibrium shift if the pressure is increased and the temperature is decreased?

Problem 49

2СО (g) СО 2 (g) + C(t); ∆H 0 ‹ 0

1. How will the rate of the direct reaction change if the volume is reduced by 7 times?

2. How many degrees must the temperature be lowered for the reaction rate to decrease by 81 times? γ = 3.

3. Write an expression for the equilibrium constant. How should the CO concentration and temperature be changed to shift the equilibrium to the right?

Problem 50

4HCl(g) + O 2 (g) 2H 2 O(g) + 2Cl 2 (g); ∆H 0 ‹ 0

1. How will the rate of the reverse reaction change if the pressure is increased by 3 times?

2. What is the temperature coefficient of the reaction, if with an increase in temperature by 10 0 C, the reaction rate changes 4 times? γ = 3.

3. Write an expression for the equilibrium constant. Where will the equilibrium shift if:

a) increase the temperature:

b) increase the volume?

Problem 51

A 2 (g) + B 2 (g) 2AB (g); ∆H 0 > 0

1. How will the rate of the reverse reaction change if the volume is reduced by 5 times?

2. How many times will the reaction rate change if the temperature is increased by 60 0 C? γ =2

3. Write an expression for the equilibrium constant. How should the concentration of A 2 and temperature be changed to shift the equilibrium to the right?

Problem 52

1. How will the rate of the direct reaction change if the pressure is increased by 4 times?

2. What is the temperature coefficient if the reaction rate changes 16 times when the temperature decreases by 20 0 C?

3. Write an expression for the equilibrium constant. How should the pressure and temperature be changed to shift the equilibrium to the right?

Problem 53

3N 2 O (g) + 2NH 3 (g) 4N 2 (g) + 3H 2 O; ∆H 0 ‹ 0

1. How will the rate of the direct reaction change if the volume is doubled?

2. How many degrees must the temperature be increased to increase the reaction rate by 32 times? γ = 2.

3. Write an expression for the equilibrium constant. Where will the equilibrium shift if:

a) increase the temperature:

b) lower the pressure?

Problem 54

CO(g) + 2H 2 (g) CH 3 OH(g); ∆H 0 › 0

1. How will the rate of the direct reaction change if the pressure is reduced by 3 times?

2. How many times will the reaction rate change if the temperature is increased by 60 0 C? γ = 2.

3. Write an expression for the equilibrium constant. Where will the equilibrium shift if the temperature and pressure are increased?

Problem 55

3O 2 (g) 2O 3 (g); ∆H 0 › 0

1. How will the rate of the reverse reaction change if the pressure is increased 7 times?

2. How many times will the reaction rate change if the temperature is increased by 30 0 C? γ = 3.

3. Write an expression for the equilibrium constant. Where will the equilibrium shift if:

a) increase the temperature:

b) lower the pressure?

Problem 56

2CO 2 (g) 2CO (g) + O 2 (g); ∆H 0 › 0

1. How will the rate of the direct reaction change if the volume is increased 6 times?

2. How many times will the reaction rate change if the temperature is increased by 50 0 C? γ = 2.

3. Write an expression for the equilibrium constant. How should the CO 2 concentration and temperature be changed so that the equilibrium shifts to the right?

Problem 57

CO 2 (g) + H 2 (g) CO (g) + H 2 O (g); ∆H 0 ‹ 0

1. How will the rate of the direct reaction change if the volume is increased by 3 times?

2. How many times will the reaction rate change if the temperature is lowered by 40 0 C? γ = 2.

3. Write an expression for the equilibrium constant. How should the volume and temperature be changed so that the equilibrium shifts to the left?

Problem 58

2SO 3 (g) 2SO 2 (g) + O 2 (g); ∆H 0 › 0

2. What is the temperature coefficient if the reaction rate changes 256 times with an increase in temperature by 40 0 C?

3. Write an expression for the equilibrium constant. Where will the equilibrium shift with increasing temperature and SO 3 concentration?

Problem 59

CO (g) + H 2 O (g) CO 2 (g) + H 2 (g); ∆Н 0<0

1. How will the speed of the direct reaction change if the volume is increased by 3 times?

2. How many times will the reaction rate change if the temperature is lowered by 40 0 C? γ= 3.

3. Write an expression for the equilibrium constant. How should volume and temperature be changed to shift the equilibrium to the left?

Problem 60

2SO 3 (g) 2SO 2 (g) + O 2 (g); ∆Н 0 >0

1. How will the rate of the direct reaction change if the pressure is increased 5 times?

2. What is the temperature coefficient if, when the temperature decreases by 30 0 C, the reaction rate changes 81 times?

3. Write an expression for the equilibrium constant. Where will the equilibrium shift with increasing temperature and SO 3 concentration?

Question:

How should the concentration of substances, temperature and pressure of the hydrogen iodide synthesis reaction H2 + I2 (=) 2Hi =+ Q be changed in order to shift the equilibrium to the right? If with explanations + best answer Save... ( and ) are arrows (=) - Reversible reaction

Answers:

1) When the temperature increases, the chemical equilibrium shifts in the direction of the endothermic reaction, and when the temperature decreases, in the direction of the exothermic reaction. This means that the temperature needs to be reduced 2) With increasing pressure, the equilibrium shifts towards the formation of substances (initial or products) with a smaller volume; when the pressure decreases, the equilibrium shifts in the direction of the formation of substances with a large volume. Here both on the left and on the right have 2 volumes (calculated by the number of moles in the equation), which means there is no influence of pressure 3) With an increase in the concentration of one of the starting substances, the equilibrium shifts in the direction of formation reaction products; When the concentration of one of the reaction products increases, the equilibrium shifts towards the formation of the starting substances. it is necessary to increase the concentration of hydrogen or iodine, or reduce the concentration of hydrogen iodide

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