Test Bank for Chemical Principles 7th Edition by Zumdahl DeCoste ISBN 1111580650 9781111580650
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Chapter 6: Chemical Equilibrium
1. A system at a state of chemical equilibrium is
A) microscopically dynamic and macroscopically dynamic.
B) microscopically dynamic and macroscopically static.
C) microscopically static and macroscopically static.
D) microscopically static and macroscopically dynamic.
E) none of these
ANS: B PTS: 1 DIF: easy TOP: 6.1
KEY: general chemistry | chemical equilibrium
2. Which of the following statements is true?
A) When two opposing processes are proceeding at identical rates, the system is at equilibrium.
B) An endothermic reaction shifts toward reactants when heat is added to the reaction.
C) The concentration of the products equals that of the reactants and is constant at equilibrium.
D) Catalysts are an effective means of changing the position of an equilibrium.
E) None of the above statements is true.
ANS: A PTS: 1 DIF: easy TOP: 6.1
KEY: general chemistry | chemical equilibrium
3. Which of the following statements concerning equilibrium is not true?
A) A system that is disturbed from an equilibrium condition responds in such a way as to restore equilibrium.
B) The value of the equilibrium constant for a given reaction mixture is the same regardless of the direction from which equilibrium is attained.
C) Equilibrium in molecular systems is dynamic, with two opposing processes balancing one another.
D) The equilibrium constant is independent of temperature.
E) A system moves spontaneously toward a state of equilibrium.
ANS: D PTS: 1 DIF: easy TOP: 6.1 | 6.2
KEY: general chemistry | chemical equilibrium
4. Indicate the mass action expression for the following reaction: 2X(g) + Y(g) 3W(g) + V(g)
C) [X]2[Y][W]3[V]
ANS: D PTS: 1 DIF: easy TOP: 6.2
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
5. If, at a given temperature, the equilibrium constant for the reaction
H2(g) + Cl2(g) 2HCl(g) is 4.2, then the equilibrium constant for the reaction
HCl(g) (1/2)H2(g) + (1/2)Cl2(g) can be represented as
A) 0.057.
B) 18.
C) 0.49.
D) 0.24.
E) 4.2.
ANS: C PTS: 1 DIF: easy TOP: 6.2
KEY: general chemistry | chemical equilibrium | equilibrium constant
6. The value of the equilibrium constant K depends on:
I. the initial concentrations of the reactants.
II. the initial concentrations of the products.
III. the final concentrations of the reactants.
IV. the final concentrations of the products.
A) II and III only
B) III and IV only
C) I and II only
D) three of these
E) none of these
ANS: E PTS: 1 DIF: easy TOP: 6.2
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
7. The value of the equilibrium constant K is dependent on:
I. the temperature of the system.
II. the nature of the reactants and products.
III. the concentration of the reactants.
IV. the concentration of the products.
A) I and II only
B) III and IV only
C) II and III only
D) three of these
E) none of these
ANS: A PTS: 1 DIF: easy TOP: 6.2
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
8. Choose the mass action or equilibrium expression for the reaction
2SO2(g) + O2(g) 2SO3(g)
A)
B)
C)
D)
E) none of these
ANS: C PTS: 1 DIF: easy TOP: 6.2
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
9. The equilibrium constant for A + 2B 3C is 1.0 10–6
Determine the equilibrium constant for 4A + 8B 12C.
A) 1.0 10–24
B) 1.0 1024
C) 1.0 10–6
D) 4 10–24
E) 4 10–6
ANS: A PTS: 1 DIF: easy TOP: 6.2
KEY: general chemistry | chemical equilibrium | equilibrium constant
10. For the hypothetical reactions 1 and 2, K1 = 102 and K2 = 10–4 . 1.
What is the value for K for reaction 3?
A) 10–2
B) 104
C) 106
D) 102
E) 10–4
ANS: B PTS: 1 DIF: moderate TOP: 6.2
KEY: general chemistry | chemical equilibrium | equilibrium constant | equilibrium
constant for the sum of reactions
11. The value of Kp for the reaction H2(g) + O2(g) H2O2(g) is 2.3 106 at 570K. Determine the value for K for this reaction at 570K.
A) 1.1 1010
B) 4.9 104
C) 1.1 108
D) 2.3 106
E) 4.3 10–7
ANS: C PTS: 1 DIF: easy TOP: 6.3
KEY: general chemistry | chemical equilibrium | equilibrium constant | the equilibrium constant Kp
12. For the reaction 2NCl3(g) N2(g) + 3Cl2(g), the equilibrium pressures are
P(NCl3) = 0.134 atm
P(N2) = 2.31 atm
P(Cl2) = 0.0510 atm
Determine Kp for this reaction.
A) 0.0171
B) 58.6
C) 9.19
D) 1.32
E) 0.879
ANS: A PTS: 1 DIF: easy TOP: 6.3
KEY: general chemistry | chemical equilibrium | equilibrium constant | the equilibrium constant Kp
13. The reaction
H2(g) + I2(g) 2HI(g) has Kp = 45.9 at 763 K. A particular equilibrium mixture at that temperature contains gaseous HI at a partial pressure of 4.30 atm and hydrogen gas at a partial pressure of 0.225 atm. What is the partial pressure of I2?
A) 1.79 atm
B) 0.225 atm
C) 0.833 atm
D) 37.1 atm
E) 0.416 atm
ANS: A PTS: 1 DIF: easy TOP: 6.3
KEY: general chemistry | chemical equilibrium | equilibrium constant | calculating equilibrium concentrations
14. For the reaction 2H2(g) + O2(g) 2H2O(g), what is the relationship between K and Kp at temperature T?
A) Kp = K(RT)2
B) K = Kp(RT)
C) K = Kp
D) Kp = K(RT)
E) K = Kp(RT)2
ANS: B PTS: 1 DIF: easy TOP: 6.3
KEY: general chemistry | chemical equilibrium | equilibrium constant | the equilibrium constant Kp
15. Consider the equation 2NOCl2(g) 2NO(g) + Cl2(g). The equilibrium constant is 0.0132 at 119°C. Calculate Kp.
A) 0.0132
B) 0.129
C) 0.425
D) 4.10 10–4
E) 43.0
ANS: C PTS: 1 DIF: easy TOP: 6.3
KEY: general chemistry | chemical equilibrium | equilibrium constant | the equilibrium constant Kp
16. For the reaction below, Kp = 1.16 at 700.°C.
CaCO3(s) CaO(s) + CO2(g)
If a 24.6-g sample of CaCO3 is put into a 14.2-L container and heated to 700.°C, what percent of the CaCO3 will react to reach equilibrium?
A) 20.6%
B) 36.9%
C) 83.9%
D) 100.%
E) 67.0%
ANS: C PTS: 1 DIF: moderate TOP: 6.3 | 6.5
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
17. At –80°C, K for the reaction
N2O4(g) 2NO2(g) is 4.66 10–8. We introduce 0.034 mol of N2O4 into a 2.5-L vessel at –80°C and let equilibrium be established. The total pressure in the system at equilibrium will be
A) 4.66 10–8 atm.
B) 0.22 atm.
C) 0.09 atm.
D) 0.43 atm.
E) 0.23 atm.
ANS: B PTS: 1 DIF: moderate TOP: 6.3 | 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
18. Consider the reaction
CaCl2(s) + 2H2O(g) CaCl2•2H2O(s)
What is the equilibrium constant for the reaction as written?
A) K = [H2O]2
B) K =
C) K =
D) K =
E) K =
ANS: D PTS: 1 DIF: easy TOP: 6.5
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
19. Consider the following equilibrium:
H2(g) + I2(s) 2HI(g) H = +68.0 kJ/mol
Which of the following is the proper Keq expression?
E)
ANS: A PTS: 1 DIF: easy TOP: 6.5
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
20. Which of the following is an example of a homogeneous equilibrium?
A) CaCl2(s) + 2H2O(g) CaCl2•2H2O(s)
B) H2(g) + I2(s) 2HI(g)
C) NH4NO3(s) N2O(g) + 2H2O(g)
D)
E) none of these
ANS: D PTS: 1 DIF: easy TOP: 6.5
KEY: general chemistry | chemical equilibrium | equilibrium constant | heterogeneous and homogeneous equilibria
21. What is the equilibrium expression for the following reaction?
NH4NO3(s) N2O(g) + 2H2O(g) A) B)
C)
D) [N2O][H2O]2
E) none of these
ANS: D PTS: 1 DIF: easy TOP: 6.5
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
22. Nitric oxide, an important pollutant in air, is formed from the elements nitrogen and oxygen at high temperatures, such as those obtained when gasoline burns in an automobile engine. At 2000°C, K for the reaction N2(g) + O2(g) 2NO(g) is 0.01.
A 1-L container originally holds 0.4 mol of N2, 0.1 mol of O2, and 0.08 mol of NO. If the volume of the container holding the equilibrium mixture of N2, O2, and NO is decreased to 0.5 L without changing the quantities of the gases present, how will their concentrations change?
A) The concentrations of N2 and O2 will increase, and the concentration of NO will decrease.
B) The concentrations of N2, O2, and NO will decrease.
C) The concentrations of N2, O2, and NO will increase.
D) There will be no change in the concentrations of N2, O2, and NO.
E) The concentration of NO will increase, and the concentrations of N2 and O2 will decrease.
ANS: C PTS: 1 DIF: easy TOP: 6.6
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | pressure change
23. For a particular system at a particular temperature, there are ______ equilibrium constant(s) and _______ equilibrium position(s).
A) one, one
B) one, an infinite number of
C) an infinite number of, one
D) an infinite number of, an infinite number of
E) none of these
ANS: B PTS: 1 DIF: easy TOP: 6.6
KEY: general chemistry | chemical equilibrium | using the equilibrium constant |
qualitatively interpreting the equilibrium constant
24. Consider the reaction
2NOBr(g) 2NO(g) + Br2(g)
A 1.0-L vessel was initially filled with pure NOBr at a pressure of 3.8 atm and 300 K. At equilibrium, the partial pressure of NOBr was 2.0 atm. Determine the value of Kp for the reaction.
A) 1.6
B) 1.4
C) 0.81
D) 0.73
E) 0.90
ANS: D PTS: 1 DIF: moderate TOP: 6.6
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
25. Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6 104
If you mixed 5.0 mol B, 0.10 mol C, and 0.0010 mol A in a 1-L container, in which direction would the reaction initially proceed?
A) To the right.
B) To the left.
C) The above mixture is the equilibrium mixture.
D) We cannot tell from the information given.
ANS: B PTS: 1 DIF: moderate TOP: 6.6
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | predicting the direction of reaction
26. Consider the following reaction:
2HF(g) H2(g) + F2(g) (K = 1.00 10–2)
Given 1.22 mol of HF(g), 0.760 mol of H2(g), and 1.09 mol of F2(g) are mixed in a 4.00-L flask, determine the reaction quotient, Q, and the net direction to achieve equilibrium.
A) Q = 0.557; the equilibrium shifts to the right.
B) Q = 0.679; the equilibrium shifts to the left.
C) Q = 0.679; the equilibrium shifts to the right.
D) Q = 0.557; the equilibrium shifts to the left.
E) Q = 1.43; the system is at equilibrium.
ANS: D PTS: 1 DIF: moderate TOP: 6.6
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | predicting the direction of reaction
27. Consider the decomposition of hydrazine as shown below.
N2H4(g) 2H2(g) + N2(g)
At a certain temperature, Kp = 2.5 103. When pure hydrazine is placed in an otherwise empty vessel at this temperature, equilibrium is reached after 30.0% of the hydrazine has decomposed. Calculate the partial pressure of hydrogen gas at equilibrium.
A) 76 atm
B) 5776 atm
C) 54 atm
D) 127 atm
E) none of these
ANS: A PTS: 1 DIF: difficult TOP: 6.6
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
28. A sample of solid NH4NO3 was placed in an evacuated container and then heated so that it decomposed explosively according to the following reaction: NH4NO3(s) N2O(g) + 2H2O(g) At equilibrium, the total pressure in the container was found to be 2.25 atm at a temperature of 500°C. Calculate Kp
A) 2.25
B) 5.06
C) 45.6
D) 1.69
E) 2.25
ANS: D PTS: 1 DIF: difficult TOP: 6.6
KEY: general chemistry | chemical equilibrium | equilibrium constant | the equilibrium constant Kp
29. Consider the following reaction:
2NOCl(g) 2NO(g) + Cl2(g) Initially pure NOCl(g) is placed in a vessel at 2.97 atm. At equilibrium, 0.416% of the NOCl has decomposed. Determine the value for Kp
A) 5.16 10–5
B) 2.70 10–8
C) 6.18 10–3
D) 1.08 10–7
E) 2.16 10–7
ANS: D PTS: 1 DIF: difficult TOP: 6.6
KEY: general chemistry | chemical equilibrium | equilibrium constant | the equilibrium constant Kp
30. Nitric oxide, an important pollutant in air, is formed from the elements nitrogen and oxygen at high temperatures, such as those obtained when gasoline burns in an automobile engine. At 2000°C, K for the reaction N2(g) + O2(g) 2NO(g) is 0.01.
Predict the direction in which the system will move to reach equilibrium at 2000°C if 0.4 mol of N2, 0.1 mol of O2, and 0.08 mol of NO are placed in a 1.0-L container.
A) The system remains unchanged.
B) The concentration of NO will decrease; the concentrations of N2 and O2 will remain unchanged.
C) The concentration of NO will decrease; the concentrations of N2 and O2 will increase.
D) The concentration of NO will increase; the concentrations of N2 and O2 will decrease.
E) More information is necessary.
ANS: C PTS: 1 DIF: easy TOP: 6.6 | 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | predicting the direction of reaction
31. Consider the following equilibrium: N2(g) + 3H2(g) 2NH3(g) with K = 2.3 10–6. 1.00 mol each of all reactants and products is placed in a 1.00-L container.
Which way will the reaction initially proceed?
A) To the right.
B) We need to know the temperature.
C) The system is at equilibrium.
D) To the left.
E) none of these
ANS: D PTS: 1 DIF: easy TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | predicting the direction of reaction
32. Consider the reaction
2SO3(g) at constant temperature. Initially a container is filled with pure SO3(g) at a pressure of 2 atm, after which equilibrium is allowed to be reached. If y is the partial pressure of O2 at equilibrium, what is the value of Kp?
A)
2SO2(g) + O2(g)
B)
C)
D)
E) none of these
ANS: B PTS: 1 DIF: moderate TOP: 6.7
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
33. Consider the following reaction (assume an ideal gas mixture).
2NOBr(g) 2NO(g) + Br2(g)
A 3.0-L vessel was initially filled with pure NOBr, at a pressure of 4.0 atm, at 300 K.
After equilibrium was established, the partial pressure of NOBr was 2.1 atm. What is Kp for the reaction?
A) 0.78
B) 0.26
C) 1.56
D) 1.72
E) 1.1
ANS: A PTS: 1 DIF: moderate TOP: 6.7
KEY: general chemistry
34. Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6 104 .
If you start with 2.0 M of chemical A, calculate the equilibrium concentration of chemical
C.
A) 8.3 10–3 M
B) 1.6 10–2 M
C) 6.25 10–5 M
D) 2.0 M
E) 0.98 M
ANS: E PTS: 1 DIF: moderate TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
35. The following reaction is investigated (assume an ideal gas mixture). 2N2O(g) + N2H4(g) 3N2(g) + 2H2O(g)
Initially there are 0.08 mol of N2O and 0.29 mol of N2H4, in a 20.0-L container. If there is 0.050 mol of N2O at equilibrium, how many moles of N2 are present at equilibrium?
A) 0.053
B) 0.045
C) 0.12
D) 0.030
E) 0.15
ANS: B PTS: 1 DIF: moderate TOP: 6.7
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
36. Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6 104 .
At a higher temperature, K = 1.8 10–5. If you start with 2.0 M of chemical A, calculate the equilibrium concentration of chemical C.
A) 2.6 10–2 M
B) 6.0 10–3 M
C) 1.0 M
D) 2.1 10–2 M
E) none of these
ANS: A PTS: 1 DIF: moderate TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
37. At a given temperature, the equilibrium constant K for the reaction
2SO2(g) + O2(g) 2SO3(g) is 3.0 109. If 2.60 mol of SO2 and 3.90 mol of O2 are placed in a 1.78-L container and allowed to react to equilibrium at this temperature, what is the concentration of SO3 at equilibrium?
A) 1.46 M
B) 0.730 M
C) 2.92 M
D) 3.65 M
E) 2.19 M
ANS: A PTS: 1 DIF: moderate TOP: 6.7
KEY: general chemistry
38. At a certain temperature, K for the reaction
2NO2 N2O4 is 7.5 L/mol. If 2.0 mol of NO2 is placed in a 2.0-liter container and permitted to react at this temperature, calculate the concentration of N2O4 at equilibrium.
A) 0.39 mol/L
B) 0.82 mol/L
C) 7.5 mol/L
D) 0.65 mol/L
E) none of these
ANS: A PTS: 1 DIF: difficult TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
Consider the following equilibrium: N2(g) + 3H2(g) 2NH3(g) with K = 2.3 10–6. 1.00 mol each of all reactants and products is placed in a 1.00-L container.
39. Calculate the equilibrium concentration of N2.
A) 1.5 M
B) 2.0 M
C) 0.5 M
D) 2.5 M
E) 1.0 M
ANS: A PTS: 1 DIF: difficult TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
40. Calculate the equilibrium concentration of H2.
A) 0.5 M
B) 1.0 M
C) 2.5 M
D) 2.0 M
E) 1.5 M
ANS: C PTS: 1 DIF: difficult TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
41. Calculate the equilibrium concentration of NH3(g).
A) 3.7 10–3 M
B) 5.4 10–5 M
C) 7.3 10–3 M
D) 4.3 10–6 M
E) none of these
ANS: C PTS: 1 DIF: difficult TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
42. 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 2.1 atm of hydrogen gas. At equilibrium, the total pressure is 2.1 atm. Calculate the partial pressure of hydrogen gas at equilibrium.
A) 2.1 atm
B) 0.0 atm
C) 1.8 atm
D) 0.60 atm
E) 0.65 atm
ANS: D PTS: 1 DIF: difficult TOP: 6.7
KEY: general chemistry | chemical equilibrium
43. Consider the equation A(aq) + 2B(aq) 3C(aq) + 2D(aq). 42.0 mL of 0.046 M A is mixed with 24.0 mL 0.105 M B. At equilibrium, the concentration of C is 0.0416 M
Calculate K.
A) 0.074
B) 4.8
C) 0.0029
D) 2.9 10–4
E) 0.033
ANS: E PTS: 1 DIF: difficult TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
44. Consider the following equilibrium:
H2(g) + I2(s) 2HI(g) H = +68.0 kJ/mol
Which of the following statements about the equilibrium is false?
A) Removing HI as it forms forces the equilibrium to the right.
B) Adding more H2(g) increases the equilibrium constant.
C) This is a heterogeneous equilibrium.
D) If the pressure on the system is increased by changing the volume, the left side is favored.
E) If the system is heated, the right side is favored.
ANS: B PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | removing products or adding reactants
45. Consider the following reaction (assume an ideal gas mixture).
2NOBr(g) 2NO(g) + Br2(g)
A 3.0-L vessel was initially filled with pure NOBr, at a pressure of 3.7 atm, at 290 K.
After equilibrium was reached, the volume was increased to 2.0 L, while the temperature was kept at 300 K. This will result in
A) a decrease in Kp.
B) a shift in the equilibrium position to the right.
C) an increase in Kp
D) a shift in the equilibrium position to the left.
E) none of these
ANS: B PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | removing products or adding reactants
46. Ammonia is prepared industrially by the following 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 statements is true?
A) Product formation (at equilibrium) is not favored as the temperature is raised.
B) K for the reaction will be larger at 500°C than at 25°C.
C) The reaction of N2 with H2 to form ammonia is endothermic.
D) At equilibrium, more NH3 is present at 500°C than at 25°C.
E) None of these is true.
ANS: A PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | temperature change
47. Given 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) depends on whether the reaction is endothermic or exothermic.
B) does not change as long as the temperature is constant.
C) does not change because A does not figure in the ratio of product to reactant.
D) decreases because A is a reactant, so the ratio of product to reactant decreases.
E) increases because when A is added, more products are made, increasing the ratio of product to reactant.
ANS: B PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | removing products or adding reactants
48. 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) endothermic
B) exothermic
C) We need more information.
ANS: A PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | temperature change
49. To increase the value of K for the exothermic reaction 2H2(g) + O2(g) H2O(g) we should
A) decrease the temperature.
B) decrease the total pressure.
C) increase the total pressure.
D) increase the temperature.
E) Two of these are necessary.
ANS: A PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | temperature change
Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6 104 .
50. Addition of chemical B to an equilibrium mixture of the above will
A) cause [A] to increase.
B) have no effect.
C) cause [C] to increase.
D) cannot be determined
E) none of these
ANS: A PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | removing products or adding reactants
51. Raising the pressure by lowering the volume of the container will
A) cause [B] to increase.
B) have no effect.
C) cause [A] to increase.
D) cannot be determined
E) none of the these
ANS: C PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | pressure change
Consider the following reaction:
PCl5 (g) PCl3(g) + Cl2(g) H = –89 kJ
52. How can the equilibrium be shifted to the right?
A) Remove Cl2.
B) Decrease the pressure by changing the volume.
C) Remove PCl3.
D) Add more PCl5.
E) Any of these will shift the equilibrium to the right.
ANS: E PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle
53. Which of the following statements is false?
A) Decreasing the volume of the container shifts the equilibrium to form more PCl5.
B) Removing PCl5 from the container shifts the equilibrium to form more PCl3
C) Adding PCl3 to the container shifts the equilibrium to form more PCl5.
D) Increasing the temperature shifts the equilibrium to form more PCl3.
ANS: B PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle
54. Which of the following statements is true?
A) Increasing the temperature of a system at equilibrium always increases the amount of product.
B) Increasing the temperature of a system at equilibrium changes the value of the equilibrium constant.
C) Increasing the temperature of a system at equilibrium always decreases the amount of product.
D) Changing the temperature of a system at equilibrium does not affect the equilibrium position.
E) none of these
ANS: B PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | temperature change
55. When the substances in the equation below are at equilibrium at pressure P and temperature
T, how can the equilibrium be shifted to favor the products?
CuO(s) + H2(g) Cu(s) + H2O(g)
Change in enthalpy = –2.0 kJ.
A) Increase the pressure by adding an inert gas such as nitrogen.
B) Allow some gas to escape at constant pressure and temperature.
C) Decrease the temperature.
D) Increase the pressure by means of a moving piston at constant temperature.
E) Add a catalyst.
ANS: C PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle
56. Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature,
K = 1.6 104 .
Placing the equilibrium mixture in an ice bath (thus lowering the temperature) will
A) have no effect.
B) cause [A] to increase.
C) cause [B] to increase.
D) cannot be determined
E) none of these
ANS: C PTS: 1 DIF: moderate TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle | temperature change
57. Explain how chemical equilibrium is microscopically dynamic and macroscopically static.
ANS: See Section 6.1 of Zumdahl, Chemical Principles
PTS: 1 DIF: moderate TOP: 6.1
KEY: general chemistry | chemical equilibrium
58. Explain how a given system at a given temperature has one equilibrium constant but an infinite number of equilibrium positions.
ANS: See Section 6.2 of Zumdahl, Chemical Principles
PTS: 1 DIF: moderate TOP: 6.2
KEY: general chemistry | chemical equilibrium | equilibrium constant | qualitatively interpreting the equilibrium constant
59. Write the equilibrium constant expression for the following reaction: CaCO3(s) CaO(s) + CO2(g)
ANS: K = [CO2]
PTS: 1 DIF: easy TOP: 6.2
KEY: general chemistry | chemical equilibrium | equilibrium constant | definition of equilibrium constant Kc
60. Derive the relationship between K and Kp
ANS: See Section 6.3 of Zumdahl, Chemical Principles
PTS: 1 DIF: moderate TOP: 6.3
KEY: general chemistry | chemical equilibrium | equilibrium constant | the equilibrium constant Kp
61. Consider the following reaction, which is involved in the catalytic destruction of ozone by chlorine atoms.
ClO(g) + O3(g) Cl(g) + 2O2(g)
Kp = 2.5 106 atm at 25° C. In an experiment at 25° C, ClO(g) at 1.0 10–3 atm was mixed with O3(g) at 2.0 10–5 atm in a rigid vessel. Calculate the equilibrium pressure of O3(g) and O2(g).
ANS: For O3, 1.3 10–17 atm; for O2, 4.0 10–5 atm
PTS: 1 DIF: moderate TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
62. At 25° C a sample of N2O4(g) is placed in an empty cylinder. After equilibrium is reached, the total pressure is 1.5 atm, and 16% (by moles) of the original N2O4 has dissociated to NO2(g). If the volume of the cylinder is increased until the total pressure is 1.0 atm, what percent (by moles) of the original N2O4(g) has dissociated at the new equilibrium position? (Hint: First calculate Kp.)
ANS: 20%
PTS: 1 DIF: moderate TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
63. In the reaction
P4(g) 2P2(g)
Kp = 0.500 atm at 1052°C. In an experiment, P4(g) is initially placed into a container at 1052°C. The total pressure of the equilibrium mixture of P4(g) and P2(g) is 6.00 atm. Calculate the equilibrium pressures of P4(g) and P2(g). Calculate the fraction (by moles) of P4(g) that has dissociated to reach equilibrium.
ANS: Pressure of P4 = 4.50 atm; Pressure of P2 = 1.50 atm; 14.3% has dissociated
PTS: 1 DIF: difficult TOP: 6.7
KEY: general chemistry | chemical equilibrium | using the equilibrium constant | calculating equilibrium concentrations
64. A mixture of O2(g) and O3(g) is present at equilibrium in a rigid container at 152 torr and 125° C. The density of the gaseous mixture is 0.228 g/L. Calculate Kp at 125° C for the reaction
3O2(g) 2O3(g)
ANS: 1.7 atm–1
PTS: 1 DIF: difficult TOP: 6.7
KEY: general chemistry | chemical equilibrium | equilibrium constant | the equilibrium constant Kp
65. State Le Châtelier’s principle.
ANS: See Section 6.8 of Zumdahl, Chemical Principles
PTS: 1 DIF: easy TOP: 6.8
KEY: general chemistry | chemical equilibrium | Le Chatelier's principle
66. At room temperature cyclohexane exists almost exclusively in the chair conformation (99.99%). But at 800°C, 30% of the cyclohexane molecules exist in the twist-boat conformation.
What is the value of the equilibrium constant for the following reaction at 800°C?
C6H12(chair) C6H12(twist-boat)
A) 0.30 D) 0.43
B) 2.3 E) 0.77
C) 0.23
ANS: D PTS: 1
The equilibration process for the reaction
4HCl(g) + O2(g) 2Cl2(g) + 2H2O(g)
is studied by initially charging a closed reaction vessel at 750 K with 2.00 atm of HCl, 1.00 atm of O2, 2.00 atm of Cl2, and 1.00 atm of H2O. At this temperature K = 1.00.
67. Once equilibrium was established, some additional chlorine gas was added to the system. This resulted in
A) no net change in the amounts of the other reaction components.
B) an increase in the amount of H2O relative to the equilibrium mixture.
C) a decrease in the amount of H2O relative to the equilibrium mixture.
D) a decrease in the amount of HCl relative to the equilibrium mixture.
E) both B and D
ANS: C PTS: 1
68. What is the partial pressure of O2 at equilibrium?
A) 2.18 atm
B) 0.91 atm
C) 1.64 atm
D) 1.18 atm
E) 2.27 atm
F) none of the above
ANS: D PTS: 1
69. At equilibrium, the partial pressure of HCl will be
A) impossible to determine with this information
B) less than 2 atm
C) zero
D) between 2 and 4 atm
E) more than 4 atm
ANS: B PTS: 1
70. To achieve equilibrium, the original reaction mixture will
A) produce more water and oxygen only
B) experience no change in component pressures
C) always move in a direction to lower the total pressure
D) shift toward products
E) shift toward reactants
ANS: D PTS: 1
71. What is the value of Q0, the reaction quotient, based on the conditions above?
A) 0.50
B) 0.125
C) 4.00
D) 1.00
E) None of the above
ANS: E PTS: 1