# Consider how temperature change affects equilibrium.

In accordance with Le Chatelier’s principle, heating causes a shift in equilibrium towards one of the two opposite processes, the course of which is accompanied by the absorption of heat. This means that 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 .

Changes in pressure also affect balance.

At a 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 mixture of gases 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 go in the direction corresponding to the decrease in the total number of moles of 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 the Le Chatelier principle, the introduction of additional amounts 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 (starting substances) causes a shift in equilibrium to the right. The addition of the reaction product(s) causes the equilibrium to shift to the left.

In which direction will the equilibrium of the reaction 2SO 2 (g) + O 2 (g) shift 2SO 3 (g); DH° <0 when temperature rises?

Solution .

Since DH°<0, heat is released during the direct reaction, which is exothermic. The reverse reaction will be endothermic. An increase in temperature always promotes the reaction with the absorption of heat, i.e. the equilibrium will shift in the direction of the original substances.

Answer: to the left.

Task 2. Given a system

N 2(g) + 3H 2(g) 2NH 3(g) ; ΔH<0.

Determine in which direction the equilibrium will shift if:

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

Decision:

The equilibrium constant of this reaction is written as follows:  .

If the pressure in the system is increased, then the volume will decrease, and the concentration of the reagents will increase. Therefore, the equilibrium shift will occur in the direction of the reaction that reduces the concentration. Since in this reaction there are 4 mol of substance on the left side of the equation, and 2 mol 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, then the equilibrium will shift to the right, in the direction of an exothermic reaction.

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

test questions

61. In what direction will the equilibrium of the system shift:

H 2(g) + 2S (tv) 2H 2 S (g) , ∆Н 0 <0,

if a) increase the temperature of the system; b) increase the concentration of hydrogen.

62. In what direction will the equilibrium in the systems shift:

a) CO (g) + Cl 2 (g) COCl 2 (g) b.) H 2 (g) + I 2 (g) 2 I (g) ,

If, at a constant temperature, the pressure is reduced by increasing the volume of the gas mixture?

63. In what direction will the equilibrium of the system shift:

C (t) + CO 2 (g) 2CO(g); ∆H0 > 0 ,

if a) lower the temperature of the system, b) lower the pressure in the system?

64. In what direction will the equilibrium of the system shift:

2SO 3 (g) 2SO 2 (g) + O 2 (g); ∆H0 > 0

if a) increase the temperature of the system, b) lower the concentration of SO 2 ?

65. In what direction will the equilibrium of the system shift:

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

a) increase the temperature; b) increase the volume?

66. How should the concentration of A 2 and temperature be changed in order to shift the equilibrium of the system to the right?

A 2 (g) + B 2 (g) 2AB(g); ∆H0 > 0

Write an expression for the equilibrium constant.

67. Write the expression for the chemical equilibrium constant for the reaction

MgCO 3 (t) MgO(t) + CO 2 (g); ∆H0 < 0 .

How can the chemical equilibrium of this reaction be shifted to the right?

68. In a state of equilibrium in the system:

N 2 (g) + 3H 2 (g) 2NH 3 (g); ∆H 0 < 0

determine in which direction the equilibrium will shift

a) with an increase in temperature; b) when the volume of the reaction vessel decreases?

69. How will the rate of forward and reverse reactions change in the system:

2SO 2 (g) + O 2 (g) 2SO 3(g); ∆Н°< 0 ,

if the volume of the reactor is doubled? Will it affect the equilibrium in the system?

70. Indicate what changes in the concentrations of reactants can shift the equilibrium of the reaction to the right:

C (t) + CO 2 (g) 2CO(g); ∆H0 > 0

71. Under what conditions is the equilibrium of the reaction:

4Fe (solid) + 3O 2 (g) 2Fe 2 O 3 (tv) ,

will shift towards the decomposition of the oxide?

72. Methanol is obtained as a result of the reaction:

CO (g) + 2H 2 (g) CH 3 OH (g); ∆Н°< 0 .

How will the equilibrium shift as

a) temperature, b) pressure?

73. How will it affect the output of chlorine in the system:

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

a) an increase in temperature in the system, b) a decrease in the total volume of the mixture,

c) decrease in oxygen concentration, d) increase in the total volume of the reactor,

e) the introduction of a catalyst?

74. In what direction will the equilibrium in the systems shift:

1) N 2 O 4 (g) 2NO 2 (g); ∆H0 > 0

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

if a) lower the temperature, b) increase the pressure?

75. In what direction will the equilibrium in the systems shift:

1) 2CO (g) + O 2 (g) 2CO 2 (g); ∆H 0 < 0 ,

2) 2N 2 (g) + O 2 (g) 2N 2 O(g) ∆H 0 > .0

if a) increase the temperature, b) decrease the pressure?

76. How will it affect the balance in the following reaction:

FeO(t) + CO(g) Fe(t) + CO 2 (g); ∆H0 > 0 ,

a) increase in temperature, b) increase in pressure?

77. In what direction will the equilibrium of the system shift:

2N 2 O 5 (g) 4NO 2 (g) + 2O 2 (g) ,

if a) increase the concentration of O 2 , b) expand the system?

78. In what direction will the equilibrium of the system shift:

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

if a) increase the temperature of the system, b) decrease the concentration of N 2 ?

79. Indicate what changes in temperature and pressure can shift the reaction equilibrium to the left:

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

80. In what direction will the equilibrium of the system shift:

A 2 (g) + 3B (g) 2C (t) + 4D (g) ; ∆N°< 0

if a) increase the temperature of the system; b) increase the pressure?

81. Indicate how it is necessary to influence the system

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

to shift the balance to the left:

a) increase the concentration of oxygen; b) increase the concentration of chlorine; c) increase the pressure; d) increase the volume of the reaction vessel?

82. In what direction will the equilibrium in the system shift

4Fe (solid) + 3O 2 (g) 2Fe 2 O 3 (tv) ,

with increasing pressure? Write an expression for the equilibrium constant.

83. What effects on the system

A(g) + B(g) AB(g); ∆H 0 < 0 ,

it is possible to increase the equilibrium concentration of the reaction product AB. Write an expression for the equilibrium constant.

84. How to change the pressure and temperature in an equilibrium system

A (t) + 2B (g) C (t) ; ∆N°< 0

to shift the balance to the right? Write an expression for the equilibrium constant.

85. In what direction will the equilibrium of the system shift:

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

if a) increase the temperature of the system; b) increase the concentration of hydrogen. Write an expression for the equilibrium constant.

86. In what direction will the equilibrium of the system shift:

3Fe (solid) + 4H 2 O (g) Fe 3 O 4 (g) + 4H 2 (g),

if: a) increase the concentration of hydrogen; b) reduce the concentration of water vapor?

87. In what direction will the equilibrium of the system shift:

N 2 (g) + 3H 2 (g) 2NH 3 (g); ∆H 0 < 0

when the temperature drops? How to explain that in practice the synthesis of ammonia is carried out at an elevated temperature?

88. How to change the volume of the reaction mixture and the temperature in an equilibrium system:

3O 2 (g) 2O 3 (g); ∆H0 > 0

to shift the balance to the right? Write an expression for the equilibrium constant

89. Calculate the equilibrium constant of the system

N 2 (g) + 3H 2 (g) 2NH 3 (g); ∆H 0 < 0,

if in equilibrium the concentration of ammonia is 0.4 mol / l, nitrogen – 0.03 mol / l, and hydrogen – 0.1 mol / l. Where will the equilibrium of the system shift with a decrease in the volume of the reaction mixture?

90. 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 Kp = 0.02.