Chemical Engineering Chapter 17 2 Magnesium hydroxide is used in several antacid formulations. When it is added to water it dissociates into magnesium and hydroxide ions

Chapter 17: Equilibrium: The Extent of Chemical Reactions

48. At high temperatures, carbon reacts with O2 to produce CO as follows:

C(s) + O2(g) 2CO(g).

When 0.350 mol of O2 and excess carbon were placed in a 5.00-L container and heated, the

equilibrium concentration of CO was found to be 0.060 M. What is the equilibrium constant, Kc,

for this reaction?

A) 0.010 B) 0.072 C) 0.090 D) 0.17 E) 1.2

49. A mixture 0.500 mole of carbon monoxide and 0.400 mole of bromine was placed into a

rigid 1.00-L container and the system was allowed to come to equilibrium. The equilibrium

concentration of COBr2 was 0.233 M. What is the value of Kc for this reaction?

CO(g) + Br2(g) COBr2(g)

A) 5.23 B) 1.22 C) 1.165 D) 0.858 E) 0.191

50. A mixture of 0.600 mol of bromine and 1.600 mol of iodine is placed into a rigid 1.000-L

container at 350°C.

Br2(g) + I2(g) 2IBr(g)

When the mixture has come to equilibrium, the concentration of iodine monobromide is 1.190

M. What is the equilibrium constant for this reaction at 350°C?

A) 3.55 × 10–3 B) 1.24 C) 1.47 D) 282 E) 325

51. The equilibrium constant Kc for the reaction

PCl3(g) + Cl2(g) PCl5(g)

is 49 at 230°C. If 0.70 mol of PCl3 is added to 0.70 mol of Cl2 in a 1.00-L reaction vessel at

230°C, what is the concentration of PCl3 when equilibrium has been established?

A) 0.049 M B) 0.11 M C) 0.30 M D) 0.59 M E) 0.83 M

52. The equilibrium constant Kc for the reaction

A(g) + B(g) C(g)

is 0.76 at 150°C. If 0.800 mol of A is added to 0.600 mol of B in a 1.00-L container at 150°C,

what will be the equilibrium concentration of C?

A) 0.19 M B) 0.29 M C) 0.36 M D) 0.41 M E) 0.51 M

53. Nitric oxide is formed in automobile exhaust when nitrogen and oxygen in air react at

high temperatures.

N2(g) + O2(g) 2NO(g)

The equilibrium constant Kp for the reaction is 0.0025 at 2127°C. If a container is charged with

8.00 atm of nitrogen and 5.00 atm of oxygen and the mixture is allowed to reach equilibrium,

what will be the equilibrium partial pressure of nitrogen?

A) 0.16 atm B) 0.31 atm C) 3.1 atm D) 7.7 atm E) 7.8 atm

Chapter 17: Equilibrium: The Extent of Chemical Reactions

54. The following reaction, in CCl4 solvent, has been studied at 25°C.

2BrCl Br2 + Cl2

The equilibrium constant Kc is known to be 0.141. If the initial concentration of chlorine is

0.0300 M and of bromine monochloride is 0.0200 M, what is the equilibrium concentration of

bromine?

A) 1.35 × 10–3 M D) 9.70 × 10–2 M

B) 2.70 × 10–3 M E) none of the above

C) 8.82 × 10–3 M

55. At 25°C, the equilibrium constant Kc for the reaction

2A(aq) B(aq) + C(aq)

is 65. If 2.50 mol of A is added to enough water to prepare 1.00 L of solution, what will the

equilibrium concentration of A be?

A) 0.038 M B) 0.14 M C) 0.28 M D) 1.18 M E) 2.4 M

56. At a certain temperature the reaction

CO2(g) + H2(g) CO(g) + H2O(g)

has Kc = 2.50. If 2.00 mol of carbon dioxide and 1.5 mol of hydrogen are placed in a 5.00 L

vessel and equilibrium is established, what will be the concentration of carbon monoxide?

A) 0.091 M B) 0.191 M C) 0.209 M D) 0.913 M E) 1.05 M

57. At 25°C, the equilibrium constant Kc for the reaction

2A(g) B(g) + C(g)

is 0.035. A mixture of 8.00 moles of B and 12.00 moles of C in a 20.0 L container is allowed to

come to equilibrium. What is the equilibrium concentration of A?

A) < 0.100 M B) 0.339 M C) 0.678 M D) 6.78 M E) 13.56 M

58. At 850°C, the equilibrium constant Kp for the reaction

C(s) + CO2(g) 2CO(g)

has a value of 10.7. If the total pressure in the system at equilibrium is 1.000 atm, what is the

partial pressure of carbon monoxide?

A) 0.362 atm B) 0.489 atm C) 0.667 atm D) 0.915 atm E) 0.921 atm

59. Ammonium iodide dissociates reversibly to ammonia and hydrogen iodide.

NH4I(s) NH3(g) + HI(g)

At 400°C, Kp = 0.215. Calculate the partial pressure of ammonia at equilibrium when a

sufficient quantity of ammonium iodide is heated to 400°C.

A) 0.103 atm B) 0.215 atm C) 0.232 atm D) 0.464 atm E) 2.00 atm

Chapter 17: Equilibrium: The Extent of Chemical Reactions

60. The reaction system

POCl3(g) POCl(g) + Cl2(g)

is at equilibrium. Which of the following statements describes the behavior of the system if

POCl is added to the container?

A) The forward reaction will proceed to establish equilibrium.

B) The reverse reaction will proceed to establish equilibrium.

C) The partial pressures of POCl3 and POCl will remain steady while the partial

pressure of chlorine increases.

D) The partial pressure of chlorine remains steady while the partial pressures of

POCl3 and POCl increase.

E) The partial pressure of chlorine will increase while the partial pressure of POCl

decreases.

61. The reaction system

POCl3(g) POCl(g) + Cl2(g)

is at equilibrium. Which of the following statements describes the behavior of the system if the

partial pressure of chlorine is reduced by 50%?

A) POCl3 will be consumed as equilibrium is established.

B) POCl will be consumed as equilibrium is established.

C) Chlorine will be consumed as equilibrium is established.

D) The partial pressure of POCl will decrease while the partial pressure of Cl2

increases as equilibrium is established.

E) The volume will have to decrease before equilibrium can be reestablished.

62. The reaction system

CS2(g) + 4H2(g) CH4(g) + 2H2S(g)

is at equilibrium. Which of the following statements describes the behavior of the system if the

partial pressure of hydrogen is doubled?

A) As equilibrium is reestablished, the partial pressure of carbon disulfide increases.

B) As equilibrium is reestablished, the partial pressure of methane, CH4, decreases.

C) As equilibrium is reestablished, the partial pressure of hydrogen decreases.

D) As equilibrium is reestablished, the partial pressure of hydrogen sulfide decreases.

E) As equilibrium is reestablished, all the partial pressures will decrease.

Chapter 17: Equilibrium: The Extent of Chemical Reactions

63. The reaction system

CS2(g) + 4H2(g) CH4(g) + 2H2S(g)

is at equilibrium. Which of the following statements describes the behavior of the system if the

partial pressure of carbon disulfide is reduced?

A) As equilibrium is reestablished, the partial pressure of carbon disulfide increases.

B) As equilibrium is reestablished, the partial pressure of hydrogen decreases.

C) As equilibrium is reestablished, the partial pressure of methane, CH4, increases.

D) As equilibrium is reestablished, the partial pressures of hydrogen and hydrogen

sulfide decrease.

E) As equilibrium is reestablished, all the partial pressures will increase.

64. Magnesium hydroxide is used in several antacid formulations. When it is added to water

it dissociates into magnesium and hydroxide ions.

Mg(OH)2(s) Mg2+(aq) + 2OH–(aq)

The equilibrium constant at 25°C is 8.9 × 10–12. One hundred grams of magnesium hydroxide is

added to 1.00 L of water and equilibrium is established. What happens to the solution if another

10 grams of Mg(OH)2 are now added to the mixture?

A) The hydroxide ion concentration will decrease.

B) The hydroxide ion concentration will increase.

C) The hydroxide ion concentration will be unchanged.

D) The solution will become supersaturated.

E) None of the above conclusions is justified without additional information.

65. Sodium hydrogen carbonate decomposes above 110°C to form sodium carbonate, water,

and carbon dioxide.

2NaHCO3(s) Na2CO3(s) + H2O(g) + CO2(g)

One thousand grams of sodium hydrogen carbonate are added to a reaction vessel, the

temperature is increased to 200°C, and the system comes to equilibrium. What happens in this

system if another 50 g of sodium carbonate are now added?

A) The partial pressure of carbon dioxide will increase.

B) The partial pressure of carbon dioxide will decrease.

C) The partial pressure of carbon dioxide will be unchanged.

D) The amounts of all products will be greater when equilibrium is reestablished.

E) None of the above conclusions is justified without knowing the equilibrium

constant.

Chapter 17: Equilibrium: The Extent of Chemical Reactions

66. Methanol can be synthesized by combining carbon monoxide and hydrogen.

CO(g) + 2H2(g) CH3OH(g)

A reaction vessel contains the three gases at equilibrium with a total pressure of 1.00 atm. What

will happen to the partial pressure of hydrogen if enough argon is added to raise the total

pressure to 1.4 atm?

A) The partial pressure of hydrogen will decrease.

B) The partial pressure of hydrogen will increase.

C) The partial pressure of hydrogen will be unchanged.

D) Kp needs to be known before a prediction can be made.

E) Both Kp and the temperature need to be known before a prediction can be made.

67. At 450°C, tert-butyl alcohol decomposes into water and isobutene.

(CH3)3COH(g) (CH3)2CCH2(g) + H2O(g)

A reaction vessel contains these compounds at equilibrium. What will happen if the volume of

the container is reduced by 50% at constant temperature?

A) The forward reaction will proceed to reestablish equilibrium.

B) The reverse reaction will proceed to reestablish equilibrium.

C) No change occurs.

D) The equilibrium constant will increase.

E) The equilibrium constant will decrease.

68. A container was charged with hydrogen, nitrogen, and ammonia gases at 120°C and the

system was allowed to reach equilibrium. What will happen if the volume of the container is

increased at constant temperature?

3H2(g) + N2(g) 2NH3(g)

A) There will be no effect.

B) More ammonia will be produced at the expense of hydrogen and nitrogen.

C) Hydrogen and nitrogen will be produced at the expense of ammonia.

D) The equilibrium constant will increase.

E) The equilibrium constant will decrease.

Chapter 17: Equilibrium: The Extent of Chemical Reactions

69. Magnesium carbonate dissociates to magnesium oxide and carbon dioxide at elevated

temperatures.

MgCO3(s) MgO(s) + CO2(g)

A reaction vessel contains these compounds in equilibrium at 300°C. What will happen if the

volume of the container is reduced by 25% at 300°C?

A) The partial pressure of carbon dioxide present at equilibrium will increase.

B) The partial pressure of carbon dioxide present at equilibrium will decrease.

C) The partial pressure of carbon dioxide at equilibrium will be unchanged.

D) The equilibrium constant will have to decrease to compensate for the decrease in

volume.

E) More information is needed in order to make a valid judgment.

70. The reaction of nitric oxide to form dinitrogen oxide and nitrogen dioxide is exothermic.

3NO(g) N2O(g) + NO2(g) + heat

What effect will be seen if the temperature of the system at equilibrium is raised by 25°C?

A) The partial pressure of NO will increase.

B) The partial pressure of NO will decrease.

C) The partial pressure of NO2 will increase.

D) The partial pressures of NO and N2O will increase.

E) All three partial pressures will increase.

71. Methanol can be synthesized by combining carbon monoxide and hydrogen.

CO(g) + 2H2(g) CH3OH(g) H°rxn = –90.7 kJ

A reaction vessel contains these compounds at equilibrium. What effect will be seen when

equilibrium is re-established after decreasing the temperature by 45°C?

A) All the partial pressures will decrease.

B) The partial pressure of methanol will decrease.

C) The partial pressures of hydrogen and methanol will decrease.

D) The partial pressure of hydrogen will increase.

E) The partial pressure of carbon monoxide will decrease.

72. Hydrogen bromide will dissociate into hydrogen and bromine gases.

2HBr(g) H2(g) + Br2(g) H°rxn = 68 kJ

What effect will a temperature increase of 50°C have on this system at equilibrium?

A) The partial pressure of hydrogen bromide will increase.

B) The partial pressure of hydrogen will increase.

C) The partial pressure of hydrogen bromide and bromine will increase.

D) There will be no effect on the partial pressure of any of the gases.

E) Need to know the initial pressure, volume, and temperature before any of the

above predictions can be made.

Chapter 17: Equilibrium: The Extent of Chemical Reactions

73. Ethane can be formed by reacting acetylene with hydrogen.

C2H2(g) + 2H2(g) C2H6(g) H°rxn = –311 kJ

Under which reaction conditions would you expect to have the greatest equilibrium yield of

ethane?

A) high temperature, high pressure

B) low temperature, high pressure

C) high temperature, low pressure

D) low temperature, low pressure

E) none of the above, unless a catalyst is present

74. Nitrogen dioxide can dissociate to nitric oxide and oxygen.

2NO2(g) 2NO(g) + O2(g) H°rxn = +114 kJ

Under which reaction conditions would you expect to produce the largest amount of oxygen?

A) high temperature, high pressure

B) low temperature, high pressure

C) high temperature, low pressure

D) low temperature, low pressure

E) none of the above, unless a catalyst is present

75. The following reaction is at equilibrium at one atmosphere, in a closed container.

NaOH(s) + CO2(g) NaHCO3(s)

Which, if any, of the following actions will decrease the total amount of CO2 gas present at

equilibrium?

A) adding N2 gas to double the pressure

B) adding more solid NaOH

C) decreasing the volume of the container

D) removing half of the solid NaHCO3

E) none of the above

76. The following reaction is at equilibrium at a pressure of 1 atm, in a closed container.

NaOH(s) + CO2(g) NaHCO3(s) H°rxn < 0

Which, if any, of the following actions will decrease the concentration of CO2 gas present at

equilibrium?

A) adding N2 gas to double the pressure D) lowering the temperature

B) adding more solid NaOH E) none of the above

C) increasing the volume of the container

Chapter 17: Equilibrium: The Extent of Chemical Reactions

77. The following reaction is at equilibrium in a closed container.

CuSO4.5H2O(s) CuSO4(s) + 5H2O(g)

Which, if any, of the following actions will lead to an increase in the pressure of H2O present at

equilibrium?

A) increasing the volume of the container

B) decreasing the volume of the container

C) adding a catalyst

D) removing some solid CuSO4

E) none of the above

78. The following reaction is at equilibrium in a sealed container.

N2(g) + 3H2(g) 2NH3(g) H°rxn < 0

Which, if any, of the following actions will increase the value of the equilibrium constant, Kc?

A) adding a catalyst D) lowering the temperature

B) adding more N2 E) none of the above

C) increasing the pressure

79. Stearic acid, nature’s most common fatty acid, dimerizes when dissolved in hexane:

2C17H35COOH (C17H35COOH)2 H°rxn = –172 kJ

The equilibrium constant for this reaction at 28°C is 2900. Estimate the equilibrium constant at

38°C.

A) 4.7 × 105 B) 2.6 × 104 C) 1.9 × 103 D) 3.2 × 102 E) 18

80. Hydrogen sulfide can be formed in the following reaction:

H2(g) +

12

S2(g) H2S(g) H°rxn = –92 kJ

The equilibrium constant Kp = 106 at 1023 K. Estimate the value of Kp at 1218 K.

A) 5.05 B) 18.8 C) 34.7 D) 88.9 E) 598

81. Write the expressions for Kc and Kp for the reaction

PH3BCl3(s) PH3(g) + BCl3(g)

82. Ammonia is synthesized in the Haber process:

N2(g) + 3H2(g) 2NH3(g)

Kp for this reaction is 1.49 × 10–5 at 500.°C. Calculate Kc at this temperature.

Chapter 17: Equilibrium: The Extent of Chemical Reactions

83. At a high temperature, the following reaction has an equilibrium constant of 1.0 × 102.

H2(g) + F2(g) 2HF(g)

If 1.00 mol of each of H2 and F2 are allowed to come to equilibrium in a 10.0 L vessel, calculate

the equilibrium amounts of H2 and HF.

84. When 0.152 mol of solid PH3BCl3 is introduced into a 3.0 L container at a certain

temperature, 8.44 × 10–3 mol of PH3 is present at equilibrium:

PH3BCl3(s) PH3(g) + BCl3(g)

Construct a reaction table for the process, and use it to calculate Kc at this temperature.

85. Consider the equilibrium

H2(g) + Br2(g) 2HBr(g)

To a 20.0 L flask are added 0.100 moles of H2 and 0.200 moles of HBr. The equilibrium

constant for this reaction is 989. Calculate the number of moles of Br2 in the flask when

equilibrium is established. Make any reasonable approximation, clearly stating what that

approximation is.

86. Consider the following gas-phase equilibrium reaction:

N2(g) + O2(g) 2NO(g) Kc = 4.10 × 10–4 at 2000°C

If 1.0 mol of NO is introduced into a 1.0 L container at 2000°C, what is the concentration of NO

when equilibrium is reached?

Chapter 17: Equilibrium: The Extent of Chemical Reactions

87. Consider the equilibrium:

A(s) B(s) + C(g) H°rxn > 0

Predict and explain how or whether the following actions would affect this equilibrium.

a. adding more solid A

b. lowering the temperature

c. increasing the pressure on the system by reducing its volume

d. adding helium gas to increase the total pressure

88. a. State Le Chatelier’s principle

b. The following reaction is at equilibrium in a closed container:

2Fe(OH)3(s) Fe2O3(s) + 3H2O(g) H°rxn > 0

What effects, if any, will the following actions have on the position of equilibrium? In each case,

state the direction of any shift in equilibrium, and give your reasons in one sentence.

(i) adding more Fe(OH)3

(ii) raising the temperature

(iii) adding a catalyst

89. The Haber process for ammonia synthesis is exothermic:

N2(g) + 3H2(g) 2NH3(g) H° = –92 kJ

If the equilibrium constant Kc for this process at 500.°C is 6.0 × 10–2, what is its value at

300.°C?

90. Although a system may be at equilibrium, the rate constants of the forward and reverse

reactions will in general be different.

91. When a reaction system reaches equilibrium, the forward and reverse reactions stop.

Chapter 17: Equilibrium: The Extent of Chemical Reactions

92. Once a reaction system reaches equilibrium, the concentrations of reactions and products

no longer change.

93. A chemical reaction will reach equilibrium when the limiting reactant is used up.

94. Increasing the initial amount of the limiting reactant in a reaction will increase the value

of the equilibrium constant, Kc.

95. In a chemical reaction, if the starting concentrations of reactants are increased, then the

equilibrium constant Kc will also increase.

96. There is a direct correlation between the speed of a reaction and its equilibrium constant.

97. If all of the coefficients in the balanced equation for an equilibrium reaction are doubled,

then the value of the equilibrium constant, Kc, will also be doubled.

98. For a gas-phase equilibrium, a change in the pressure of any single reactant or product

will change Kp.

99. If all the reactants and products in an equilibrium reaction are in the gas phase, then Kp =

Kc.

100. For a gas-phase equilibrium, a change in the pressure of any single reactant or product

will affect the amounts of other substances involved in the equilibrium.

101. For a solution equilibrium, a change in concentration of a reactant or product does not

change Kc.

102. For some gas-phase reactions, Kp = Kc.

103. If Q > K, more products need to be formed as the reaction proceeds to equilibrium.

Chapter 17: Equilibrium: The Extent of Chemical Reactions

104. Changing the amount of a solid reactant or product in an equilibrium reaction will not

affect the amounts of the other reactants and products present at equilibrium.

105. Unless H°rxn = 0, a change in temperature will affect the value of the equilibrium

constant Kc.

106. A good catalyst for a reaction will speed up the forward reaction and slow down the

reverse reaction.