Consider how a change in temperature affects equilibrium. Consider how temperature change affects equilibrium Examples of problem solving

How to change the pressure, volume, and concentration of reactants in the system CO (g) + H 2 O (g) «CO 2 (g) + H 2 (g)) in order to increase the yield of reaction products? Determine the ΔН sign of the reverse reaction if it is known that the equilibrium has shifted to the right with increasing temperature.

Decision

Since both the right and the left have the same number of moles of gaseous substances (1 + 1 \u003d 1 + 1), a change in pressure and volume will not affect the equilibrium position. And in order to increase the yield of the reaction products (shift the equilibrium to the right), it is necessary either to increase the concentration of the initial substances CO (g) and H 2 O (g) (the rate of the direct reaction will increase and these substances will begin to be consumed), or to reduce the concentration of the products, i.e. to remove CO 2 (g) and H 2 (g) from the reaction zone (the rate of the reverse reaction will decrease and these substances will begin to form).

Since it is known that with an increase in temperature the equilibrium shifted to the right, it can be concluded that this reaction will be endothermic, and the reverse, respectively, will be exothermic, i.e., ΔH of the reverse reaction.< 0.

Based on the law of mass action

Example

The reaction proceeds according to the equation 2H 2 + O 2 «2H 2 O. In what direction will the chemical equilibrium shift if the pressure is increased by 4 times? Confirm the answer with calculations.

Decision:

Let's write down the formula for the law of mass action for direct and reverse reactions. Since the system is homogeneous, then u 1 is a straight line \u003d k 2 and u 1 is an inverse \u003d k 2.

When the pressure increases by 4 times, the concentrations of all substances will also increase by 4 times. Then u 2 direct \u003d k 2 \u003d 64 k 2 and u 2 inverse \u003d k 2 \u003d 16 k 2 Thus, the speed of the forward reaction increased 64 times, and the reverse - only 16 times: u 2pr / u 2rev \u003d 64/16 \u003d 4 This means that the chemical equilibrium will shift towards the direct reaction, since the speed of the direct reaction increases more times.

3 Tasks for independent solution:

3.1 Speed

3.1.1 The reaction proceeds according to the equation 2NO + Cl 2 \u003d 2NOCl. The concentrations of the starting materials before the start of the reaction were \u003d 0.04 mol / L, \u003d 0.01 mol / L. Calculate the concentration of these substances at the moment when \u003d 0.005 mol / L.

3.1.2 Oxidation of sulfur and its dioxide proceeds according to the equation:

a) S (k) + O 2 (g) \u003d SO 2 (g); b) 2SO 2 (d) + O 2 (d) \u003d 2SO 3 (d).

How do the rates of these reactions change if the volumes of each of the systems are quadrupled?

3.1.3 The reaction proceeds according to the equation Н 2 + Br 2 \u003d 2HBr. The rate constant of this reaction at a certain temperature is 0.2. Initial concentrations of reactants: \u003d 0.08 mol / l, \u003d 0.06 mol / l. Calculate the initial reaction rate and its rate when \u003d 0.05 mol / L.

3.1.4 How will the reaction rate change 2NO (g) + O 2 (g) \u003d 2NO 2 (g) if: a) increase the pressure in the system by 4 times; b) lower the NO concentration by 5 times? Explain the answer.

3.1.5 How should the temperature be changed in order to reduce the rate of a homogeneous reaction by a factor of 27 at a temperature coefficient of 3?

3.1.6 How will the rate of the homogeneous reaction 2NO + O 2 «2NO 2 change if the concentration is increased by 3 times, and the concentration is decreased by 4 times?

Question:

How should the concentration of substances, the temperature and pressure of the reaction for the synthesis of hydrogen iodide H2 + I2 (\u003d) 2Hi \u003d + Q be changed in order to shift the equilibrium to the right? If with explanations + the best answer Save ... (and) are arrows (\u003d) - Reversible reaction

Answers:

1) With increasing temperature, chemical equilibrium shifts in the direction of the endothermic reaction, with decreasing temperature, in the direction of the exothermic reaction. This means that you need to reduce the temperature 2) When the pressure rises, the equilibrium shifts in the direction of the formation of substances (initial or products) with a smaller volume; with decreasing pressure, the equilibrium shifts in the direction of the formation of substances with a large volume Here, on the left and on the right, 2 volumes (calculated by the number of moles in the equation), which means there is no pressure effect 3) With an increase in the concentration of one of the initial substances, the equilibrium shifts in the direction of formation reaction products; with an increase in the concentration of one of the reaction products, the equilibrium shifts in the direction of the formation of the starting materials. it is necessary to increase the concentration of hydrogen or iodine, or reduce the concentration of hydrogen iodide

Similar questions

• Mini-project "World of professions" According to working conditions, groups of professions related to work are distinguished: indoors, outdoors, in small confined spaces (cabins), in unusual working conditions Classify the following professions according to working conditions: accountant, steelmaker, postman , crane operator, rescuer, teacher, shepherd, huntsman, cashier of the exchange office, serviceman, driver, diver, miner, cosmonaut, field operator, manager, stuntman ..

In accordance with Le Chatelier's principle, heating causes a shift in equilibrium towards one of the two counter processes, the course 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 the process, the course of which is accompanied by the release of heat ... Cooling favors the exothermic process and causes an increase in its equilibrium constant.

Pressure changes also affect balance.

At constant temperature, the equilibrium constant does not change under the influence of pressure. However, the relative amounts of starting materials and products under pressure change in the direction predicted by Le Chatelier's principle. If the pressure is increased 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 the gases present (in the direction of decreasing concentration). With a decrease in pressure, the equilibrium will shift towards the reaction with a large number of moles.

Equilibrium is also affected by changes in concentration.

In accordance with Le Chatelier's principle, the introduction of additional amounts of a reagent into an equilibrium system causes a shift in the equilibrium in the direction at which its concentration decreases. Therefore, an excess of the starting substance (starting substances) 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

Objective 1.Given a 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.

Decision:In accordance with the law of action of masses, we write down the expressions for the speed of the 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 the new expressions for the reaction rates:

Consequently, the speed of the direct reaction will increase in

.

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

.

If the pressure in the system is increased, then the volume will decrease, and the concentration of reagents will increase. Therefore, a shift in equilibrium will occur in the direction of a reaction that decreases concentration. Since in this reaction there are 4 moles of matter 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 goes with the release of heat. If we lower the temperature, then the equilibrium will shift to the right, towards the exothermic reaction.

With an increase in the hydrogen concentration, the equilibrium will shift towards the reaction that decreases the hydrogen concentration, in this case to the right.

Objective 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?

Decision.

According to the law of mass action, the initial reaction rate is v n \u003d k × 2. After reducing the hydrogen concentration by 3 times, the speed will be equal to v к \u003d k × (1/3) 2 2 \u003d 1 / 9k 2. ... After changing the hydrogen concentration, the speed will change as follows: v k / v n \u003d 1 / 9k 2 / k 2 \u003d 1/9. Answer: the reaction rate will decrease by 9 times.

Objective 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?

Decision.

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: to the left.

Problem 4.How will the reaction rate change when the temperature rises from 20 0 С to 60 0 С, if the temperature coefficient of the reaction rate is 2?

Decision: To solve the problem, 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 this reaction will end if it is carried out at 70 0 С?

Decision: Using the Van't Hoff rule, we calculate how many times the reaction rate will change.

; sstarts attitude:.

The reaction rate 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 under Nos. 31-45, the equations of reactions in a state of equilibrium are given. Solve the problem according to the condition.

Assignment 31

2H 2 (g) + O 2 (g) 2H 2 O (g); ; ∆H °

1. How will the speed 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 С? γ \u003d 2.

Assignment 32

A (t) + 2B (g) C (t); ∆H °

2. How many times will the reaction rate change if the temperature is increased by 20 0 С? γ \u003d 2.

Assignment 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 hydrogen concentration is increased by 3 times?

2. How many times will the reaction rate change if the temperature is lowered by 30 0 С? γ \u003d 4.

a) increase the temperature;

b) lower the pressure?

Assignment 34

A 2 (g) + 3B (g) 2C (t) + 4D (g); ∆H °

1. How will the speed 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 С? γ \u003d 3.

Assignment 35

2SO 2 (g) + O 2 (g) 2SO 3 (g); ∆H °

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 reduced by 2 times?

2. How many times will the reaction rate change if the temperature is increased by 30 0 С? γ \u003d 2.

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

a) lower the temperature;

b) increase the pressure?

Assignment 36

N 2 (g) + 3H 2 (g) 2NH 3 (g); ∆H 0< 0

1. How will the speed 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 \u200b\u200bС, and the reaction rate changed 81 times?

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

a) increase the concentration of N 2;

b) reduce the temperature?

Assignment 37

FeO (t) + CO (g) Fe (t) + CO 2 (g); ∆H 0\u003e 0

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

2. How many times will the reaction rate change if the temperature is increased by 10 0 С? γ \u003d 3.

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

Assignment 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 has changed 8 times when the temperature drops by 30 0 С?

3. Write the expression for the equilibrium constant. Where will the equilibrium shift with decreasing temperature and decreasing CO2 concentration?

Assignment 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 \u200b\u200bС? γ \u003d 3

3. Write the expression for the equilibrium constant. Where will the equilibrium shift with decreasing temperature and pressure?

Assignment 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 HCl concentration is reduced by 2 times, and the O 2 concentration is increased by 8 times?

2. How many times will the reaction rate change if the temperature is lowered by 50 0 С? γ \u003d 2

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

Assignment 41

N 2 O 4 (g) 2NO 2 (g); ∆H 0\u003e 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, when the temperature drops by 10 0 С, the reaction rate changes 2 times?

3. Write the expression for the equilibrium constant. How do you change the pressure and temperature to shift the equilibrium to the left?

Assignment 42

2AB (d) A 2 (d) + 2B (d); ∆H 0\u003e 0

1. How will the rate of the reverse reaction change if the concentration of А \u200b\u200b2 is reduced by 5 times?

2. How many degrees should the temperature be increased if the reaction rate has changed 8 times? Γ \u003d 2

3. Write the expression for the equilibrium constant. How do you change the pressure and temperature to shift the equilibrium to the right?

Assignment 43

C (t) + CO 2 (g) 2CO (g); ∆H 0\u003e 0

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

2. How many degrees should the temperature be lowered for the reaction rate to change 16 times? γ \u003d 2.

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

Assignment 44

2CO (g) + O 2 (g) 2CO 2 (g); ∆H 0 ‹0

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

2. How many degrees do you need to raise the temperature to speed up the reaction 64 times? γ \u003d 2.

3. Write the expression for the equilibrium constant. How do you change the volume and temperature to move the equilibrium to the left?

Assignment 45

N 2 (g) + O 2 (g) 2NO (g); ∆H 0 ›0

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

2. How many degrees do you need to lower the temperature so that the reaction rate decreases 27 times? γ \u003d 3

3. Write the expression for the equilibrium constant. How do you change the pressure and temperature to shift the equilibrium to the right?

Assignment 46

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

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

2. How many degrees do you need to raise the temperature to speed up the reaction 27 times? γ \u003d 3

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

a) lower the temperature:

b) increase the pressure?

Assignment 47

2NO (g) + O 2 (g) 2NO 2 (g); ∆H 0 ‹0

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

2. How many degrees should the temperature be lowered so that the reaction rate decreases 64 times? γ \u003d 3

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

Assignment 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 decreased by 2 times?

2. How many degrees do you need to raise the temperature for the reaction rate to increase 9 times? γ \u003d 3.

3. Write the expression for the equilibrium constant. Where will the equilibrium shift if the pressure increases and the temperature decreases?

Assignment 49

2CO (g) CO 2 (g) + C (t); ∆H 0 ‹0

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

2. How many degrees do you need to lower the temperature so that the reaction rate decreases 81 times? γ \u003d 3.

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

Assignment 50

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

1. How will the speed 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 С, the reaction rate will change 4 times? γ \u003d 3.

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

a) increase the temperature:

b) increase the volume?

Assignment 51

A 2 (g) + B 2 (g) 2AB (g); ∆H 0\u003e 0

1. How will the speed 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 С? γ \u003d 2

3. Write the expression for the equilibrium constant. How should the A2 concentration and temperature be changed in order to shift the equilibrium to the right?

Assignment 52

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

2. What is the temperature coefficient if the reaction rate has changed 16 times with a decrease in temperature by 20 0 С?

3. Write the expression for the equilibrium constant. How do you change the pressure and temperature to shift the equilibrium to the right?

Assignment 53

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

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

2. How many degrees do you need to raise the temperature to speed up the reaction 32 times? γ \u003d 2.

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

a) increase the temperature:

b) lower the pressure?

Assignment 54

CO (g) + 2H 2 (g) CH 3 OH (g); ∆H 0 ›0

1. How will the speed 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 С? γ \u003d 2.

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

Assignment 55

3O 2 (g) 2O 3 (g); ∆H 0 ›0

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

2. How many times will the reaction rate change if the temperature is increased by 30 0 С? γ \u003d 3.

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

a) increase the temperature:

b) lower the pressure?

Assignment 56

2CO 2 (g) 2CO (g) + O 2 (g); ∆H 0 ›0

1. How will the speed 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 С? γ \u003d 2.

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

Assignment 57

CO 2 (g) + H 2 (g) CO (g) + H 2 O (g); ∆H 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 \u200b\u200bС? γ \u003d 2.

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

Assignment 58

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

2. What is the temperature coefficient if the reaction rate has changed 256 times when the temperature rises by 40 0 \u200b\u200bС?

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

Assignment 59

CO (g) + H 2 O (g) CO 2 (g) + H 2 (g); ∆H 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 \u200b\u200bС? γ \u003d 3.

3. Write the expression for the equilibrium constant. How do you change the volume and temperature to move the equilibrium to the left?

Assignment 60

2SO 3 (g) 2SO 2 (g) + O 2 (g); ∆Н 0\u003e 0

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

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

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