Chapter 13 2 what is the value of the equilibrium constant

KEY: Chemistry | general chemistry | chemical equilibrium MSC: Quantitative

47. Initially 2.0 moles of N2(g) and 4.0 moles of H2(g) were added to a 1.0-liter container and

the following reaction then occurred:

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

The equilibrium concentration of NH3(g) = 0.55 moles/liter at 700.°C. The value for K at

700.°C for the formation of ammonia is:

A)

1.0  10–1

B)

5.5  10–2

C)

5.5  10–3

D)

3.0  10–1

E)

none of these

Consider the following reaction (assume an ideal gas mixture): 2NOBr(g) 2NO(g) +

Br2(g) A 1.0-liter vessel was initially filled with pure NOBr, at a pressure of 4.0 atm, at

300 K.

48. After equilibrium was established, the partial pressure of NOBr was 3.1 atm. What is Kp for

the reaction?

A)

0.26

B)

0.038

C)

0.13

D)

0.45

E)

none of these

49. After equilibrium was reached, the volume was increased to 2.0 liters, while the temperature

was kept at 300 K. The result of this change was

A)

an increase in Kp

B)

a decrease in Kp

C)

a shift in the equilibrium position to the right

D)

a shift in the equilibrium position to the left

E)

none of these

50. Nitrogen gas (N2) reacts with hydrogen gas (H2) to form ammonia (NH3). At 200°C in a

closed container, 1.0 atm of nitrogen gas is mixed with 2.0 atm of hydrogen gas. At

equilibrium, the total pressure is 2.2 atm. Calculate the partial pressure of hydrogen gas at

equilibrium.

A)

2.2 atm

B)

0.80 atm

C)

1.4 atm

D)

0.0 atm

E)

none of these

51. The following reaction is investigated (assume an ideal gas mixture):

2N2O(g) + N2H4(g) 3N2(g) + 2H2O(g)

Initially there are 0.10 moles of N2O and 0.25 moles of N2H4, in a 10.0-L container. If there

are 0.048 moles of N2O at equilibrium, how many moles of N2 are present at equilibrium?

A)

2.6  10–2

B)

5.2  10–2

C)

7.8  10–2

D)

1.6  10–1

E)

none of these

52. A 3.00-liter flask initially contains 3.00 mol of gas A and 1.50 mol of gas B. Gas A

decomposes according to the following reaction:

3A 2B + C

The equilibrium concentration of gas C is 0.115 mol/L. Determine the equilibrium

concentration of gas A.

A)

0.115 M

B)

0.655 M

C)

0.730 M

D)

0.885 M

E)

0.345 M

53. A 3.00-liter flask initially contains 3.00 mol of gas A and 1.50 mol of gas B. Gas A

decomposes according to the following reaction:

3A 2B + C

The equilibrium concentration of gas C is 0.119 mol/L. Determine the equilibrium

concentration of gas B.

A)

0.119 M

B)

0.619 M

C)

0.738 M

D)

0.262 M

E)

0.238 M

54. A 3.00-liter flask initially contains 3.00 mol of gas A and 1.50 mol of gas B. Gas A

decomposes according to the following reaction:

3A 2B + C

The equilibrium concentration of gas C is 0.146 mol/L. Determine the value of the

equilibrium constant, K.

A)

0.206

B)

0.163

C)

3.84  10–3

D)

0.516

E)

none of these

55. A sample of solid NH4NO3 was placed in an evacuated container and then heated so that it

decomposed explosively according to the following equation:

NH4NO3(s) N2O(g) + 2H2O(g)

At equilibrium the total pressure in the container was found to be 2.63 atm at a temperature

of 500.°C. Calculate Kp.

A)

0.769

B)

1.54

C)

0.674

D)

2.70

E)

72.8

Given the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6  104.

56. If you mixed 5.0 mol B, 0.10 mol C, and 0.0010 mol A in a one-liter container, which

direction would the reaction initially proceed?

A)

To the left.

B)

To the right.

C)

The above mixture is the equilibrium mixture.

D)

Cannot tell from the information given.

E)

None of these (A-D).

57. Addition of chemical B to an equilibrium mixture of the above will

A)

cause [A] to increase

B)

cause [C] to increase

C)

have no effect

D)

cannot be determined

E)

none of the above

58. At a higher temperature, K = 1.8  10–5. Placing the equilibrium mixture in an ice bath (thus

lowering the temperature) will

A)

cause [A] to increase

B)

cause [B] to increase

C)

have no effect

D)

cannot be determined

E)

none of the above

59. Raising the pressure by lowering the volume of the container will

A)

cause [A] to increase

B)

cause [B] to increase

C)

have no effect

D)

cannot be determined

E)

none of the above

Consider the following equilibrium: 2NOCl(g) 2NO(g) + Cl2(g) with K = 1.6  10–5.

In an experiment, 1.00 mole of pure NOCl and 1.00 mole of pure Cl2 are placed in a 1.00-L

container.

60. If x moles of NOCl react, what is the equilibrium concentration of NO?

A)

x

B)

2x

C)

–x

D)

–2x

E)

x2

61. If x moles of NOCl react, what is the equilibrium concentration of Cl2?

A)

x

B)

x

C)

1 + x

D)

1 + x

E)

1 + 2x

62. At a certain temperature K for the reaction 2NO2 N2O4 is 7.5 liters/mole. If 2.0 moles

of NO2 are placed in a 2.0-liter container and permitted to react at this temperature, calculate

the concentration of N2O4 at equilibrium.

A)

0.39 moles/liter

B)

0.65 moles/liter

C)

0.82 moles/liter

D)

7.5 moles/liter

E)

none of these

63. Exactly 1.0 mol N2O4 is placed in an empty 1.0-L container and is allowed to reach

equilibrium described by the equation N2O4(g) 2NO2(g)

If at equilibrium the N2O4 is 37% dissociated, what is the value of the equilibrium constant,

Kc, for the reaction under these conditions?

A)

1.2

B)

0.87

C)

1.2

D)

0.55

E)

0.22

64. At 500.0 K, one mole of gaseous ONCl is placed in a one-liter container. At equilibrium it is

5.3% dissociated according to the equation shown here: 2ONCl 2NO + Cl2. Determine

the equilibrium constant.

A)

8.3  10–5

B)

1.6  10–3

C)

5.6  10–2

D)

9.5  10–1

E)

1.2  104

65. Consider the following equilibrium:

2NOCl(g) 2NO(g) + Cl2(g)

with K = 1.6  10–5. 1.00 mole of pure NOCl and 0.958 mole of pure Cl2 are placed in a

1.00-L container. Calculate the equilibrium concentration of NO(g).

A)

2.04  10–3 M

B)

9.58  10–1 M

C)

1.04 M

D)

5.78  10–3 M

E)

4.09  10–3 M

66. Consider the following equilibrium:

2NOCl(g) 2NO(g) + Cl2(g)

with K = 1.6  10–5. 1.00 mole of pure NOCl and 0.964 mole of pure Cl2 are placed in a

1.00-L container. Calculate the equilibrium concentration of Cl2(g).

A)

1.6  10–5 M

B)

0.966 M

C)

0.483 M

D)

2.04  10–3 M

E)

4.07  10–3 M

67. For the reaction below, Kp = 1.16 at 800.°C.

CaCO3(s) CaO(s) + CO2(g)

If a 31.3-gram sample of CaCO3 is put into a 10.0-L container and heated to 800.°C, what

percent of the CaCO3 will react to reach equilibrium?

A)

21.8%

B)

42.1%

C)

56.5%

D)

100.0%

E)

none of these

68. At –80°C, K for the reaction

N2O4(g) 2NO2(g)

is 4.66  10–8. We introduce 0.047 mole of N2O4 into a 1.0-L vessel at –80°C and let

equilibrium be established. The total pressure in the system at equilibrium will be:

A)

0.31 atm

B)

0.74 atm

C)

1.4 atm

D)

0.047 atm

E)

none of these

69. The equilibrium system 2A 2B + C has a very small equilibrium constant:

K = 2.6  10–6.

Initially 3.0 moles of A are placed in a 1.5-L flask. Determine the concentration of C at

equilibrium.

A)

0.011 M

B)

0.024 M

C)

0.032 M

D)

0.048 M

E)

2.0 M

70. Which of the following statements concerning equilibrium is not true?

A)

A system that is disturbed from an equilibrium condition responds in a manner to

restore equilibrium.

B)

Equilibrium in molecular systems is dynamic, with two opposing processes

balancing one another.

C)

The value of the equilibrium constant for a given reaction mixture is the same

regardless of the direction from which equilibrium is attained.

D)

A system moves spontaneously toward a state of equilibrium.

E)

The equilibrium constant is independent of temperature.

The questions below refer to the following system:

Co(H2O)62+ + 4 Cl– CoCl42– + 6H2O

(pink)

(blue)

When cobalt(II) chloride is added to pure water, the Co2+ ions hydrate. The hydrated form

then reacts with the Cl– ions to set up the equilibrium shown here.

71. Which statement below describes the change that the system will undergo if hydrochloric

acid is added?

A)

It should become more blue.

B)

It should become more pink.

C)

The equilibrium will shift to the right.

D)

The equilibrium will shift to the left.

E)

Two of these.

72. Which statement below describes the change that the system will undergo if water is added?

A)

More chloride ions will be produced.

B)

More water will be produced.

C)

The equilibrium will shift to the right.

D)

The color will become more blue.

E)

There will be less of the hydrated cobalt ion at the new equilibrium position.

73. Which statement below describes the change that the system will undergo if silver nitrate is

added?

A)

It should become more blue.

B)

It should become more pink.

C)

Water will be produced.

D)

The silver ion will react with the CoCl42–.

E)

Nothing will change.

The following questions refer to the equilibrium shown here: 4NH3(g) + 5O2(g)

4NO(g) + 6H2O(g)

74. What would happen to the system if oxygen were added?

A)

More ammonia would be produced.

B)

More oxygen would be produced.

C)

The equilibrium would shift to the right.

D)

The equilibrium would shift to the left.

E)

Nothing would happen.

75. What would happen to the system if the pressure were decreased?

A)

Nothing would happen.

B)

More oxygen would be produced.

C)

The water vapor would become liquid water.

D)

The ammonia concentration would increase.

E)

The NO concentration would increase.

76. For a certain reaction at 25.0°C, the value of K is 1.2  10–3. At 50.0°C the value of K is

3.4  10–1. This means that the reaction is

A)

exothermic

B)

endothermic

C)

never favorable

D)

more information needed

E)

none of these (A-D)

77. Ammonia is prepared industrially by the reaction: N2(g) + 3H2(g) 2NH3(g) for the

reaction: H° = –92.2 kJ and K (at 25°C) = 4.0  108. When the temperature of the reaction

is increased to 500°C, which of the following is true?

A)

K for the reaction will be larger at 500°C than at 25°C.

B)

At equilibrium, more NH3 is present at 500°C than at 25°C.

C)

Product formation (at equilibrium) is not favored as the temperature is raised.

D)

The reaction of N2 with H2 to form ammonia is endothermic.

E)

None of the above is true.

Consider the following equilibrium: 2H2(g) + X2(g) 2H2X(g) + energy

78. Addition of X2 to a system described by the above equilibrium

A)

will cause [H2] to decrease

B)

will cause [X2] to decrease

C)

will cause [H2X] to decrease

D)

will have no effect

E)

cannot possibly be carried out

79. Addition of argon to the above equilibrium

A)

will cause [H2] to decrease

B)

will cause [X2] to increase

C)

will cause [H2X] to increase

D)

will have no effect

E)

cannot possibly be carried out

80. Increasing the pressure by decreasing the volume will cause

A)

the reaction to occur to produce H2X

B)

the reaction to occur to produce H2 and X2

C)

the reaction to occur to produce H2 but no more X2

D)

no reaction to occur

E)

X2 to dissociate

81. Increasing the temperature will cause

A)

the reaction to occur to produce H2X

B)

the reaction to occur to produce H2 and X2

C)

the reaction to occur to produce H2 but no more X2

D)

no reaction to occur

E)

an explosion

82. Which of the following statements is true?

A)

When two opposing processes are proceeding at identical rates, the system is at

equilibrium.

B)

Catalysts are an effective means of changing the position of an equilibrium.

C)

The concentration of the products equals that of reactants and is constant at

equilibrium.

D)

An endothermic reaction shifts toward reactants when heat is added to the reaction.

E)

None of the above statements is true.

83. Consider the following system at equilibrium: N2(g) + 3H2(g) 2NH3(g) + 92.94 kJ

Which of the following changes will shift the equilibrium to the right?

I.

increasing the temperature

II.

decreasing the temperature

III.

increasing the volume

IV.

decreasing the volume

V.

removing some NH3

VI.

adding some NH3

VII.

removing some N2

VIII.

adding some N2

A)

I, IV, VI, VII

B)

II, III, V, VIII

C)

I, VI, VIII

D)

I, III, V, VII

E)

II, IV, V, VIII

84. Consider the reaction A(g) + B(g) C(g) + D(g). You have the gases A, B, C, and D at

equilibrium. Upon adding gas A, the value of K:

A)

increases, because by adding A more products are made, increasing the product to

reactant ratio

B)

decreases, because A is a reactant so the product to reactant ratio decreases

C)

does not change, because A does not figure into the product to reactant ratio

D)

does not change, as long as the temperature is constant

E)

depends on whether the reaction is endothermic or exothermic

85. Consider the combustion of methane (as represented by the following equation). This is the

reaction that occurs for a Bunsen burner, which is a source of heat for chemical reactions in

the laboratory.

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

For the system at chemical equilibrium, which of the following explains what happens if the

temperature is raised?

A)

The equilibrium position is shifted to the right and the value for K increases.

B)

The equilibrium position is shifted to the right and the value for K decreases.

C)

The equilibrium position is shifted to the left and the value for K decreases.

D)

The equilibrium position is shifted to the left and the value for K increases.

E)

The equilibrium position is shifted but the value for K stays constant.

86. Consider the reaction represented by the equation 2SO2(g) + O2(g) 2SO3(g). For the

system at chemical equilibrium, which of the following explains what happens after the

addition of oxygen gas (assume constant temperature)?

A)

The amount of SO3(g) increases and the value for K increases.

B)

The amount of SO3(g) decreases and the value for K increases.

C)

The amount of SO3(g) stays the same and the value for K decreases.

D)

The amount of SO3(g) decreases and the value for K stays the same.

E)

The amount of SO3(g) increases and the value for K stays the same.

87. Consider the reaction represented by the equation: N2(g) + 3H2(g) 2NH3(g). What

happens to the equilibrium position when an inert gas is added to this system (as represented

above) at equilibrium?

A)

If the container is rigid, nothing happens to the equilibrium position. If the

container is fitted with a moveable piston, the equilibrium position shifts.

B)

If the container is rigid, the equilibrium position shifts. If the container is fitted

with a moveable piston, nothing happens to the equilibrium position.

C)

The equilibrium position shifts no matter what the container is like.

D)

Nothing happens to the equilibrium position no matter what the container is like.

E)

The value of the equilibrium constant must be known to answer this question.