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Chapter 13: Chemical Equilibrium
MULTIPLE CHOICE
1. Which of the following is true about a system at equilibrium?
A)
The concentration(s) of the reactant(s) is equal to the concentration(s) of the
product(s).
B)
No new product molecules are formed.
C)
The concentration(s) of reactant(s) is constant over time.
D)
The rate of the reverse reaction is equal to the rate of the forward reaction and both
rates are equal to zero.
E)
None of the above (A-D) is true.
2. Which of the following is true about chemical equilibrium?
A)
It is microscopically and macroscopically static.
B)
It is microscopically and macroscopically dynamic.
C)
It is microscopically static and macroscopically dynamic.
D)
It is microscopically dynamic and macroscopically static.
E)
None of these are true about chemical equilibrium.
3. Equilibrium is reached in chemical reactions when:
A)
The rates of the forward and reverse reactions become equal.
B)
The concentrations of reactants and products become equal.
C)
The temperature shows a sharp rise.
D)
All chemical reactions stop.
E)
The forward reaction stops.
4. For a particular system at a particular temperature there ______ equilibrium constant(s) and
there _______ equilibrium position(s).
A)
are infinite; is one
B)
is one; are infinite
C)
is one; is one
D)
are infinite; are infinite
E)
none of these
5. For the reaction given below, 2.00 moles of A and 3.00 moles of B are placed in a 6.00-L
container.
At equilibrium, the concentration of A is 0.246 mol/L. What is the concentration of B at
equilibrium?
A)
0.246 mol/L
B)
0.325 mol/L
C)
0.500 mol/L
D)
0.492 mol/L
E)
none of these
6. 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, II
B)
II, III
C)
III, IV
D)
It is dependent on three of the above choices.
E)
It is not dependent on any of the above choices.
7. If the equilibrium constant for A + B C is 0.208, then the equilibrium constant for
2C 2A + 2B is
A)
0.584
B)
4.81
C)
0.416
D)
23.1
E)
0.208
8. Indicate the mass action expression for the following reaction: 2X(g) + Y(g) 3W(g) +
V(g)
A)
[X]2[Y][W]3[V]
B)
C)
D)
E)
none of these
9. If, at a given temperature, the equilibrium constant for the reaction
H2(g) + Cl2(g) 2HCl(g) is Kp, then the equilibrium constant for the reaction
HCl(g) → H2(g) + Cl2 (g) can be represented as:
A)
B)
Kp2
C)
D)
E)
none of these
10. Apply the law of mass action to determine the equilibrium expression for 2NO2Cl(aq)
2NO2(aq) + Cl2(aq).
A)
K = 2[NO2][Cl2]/2[NO2Cl]
B)
K = 2[NO2Cl]/2[NO2][Cl2]
C)
K = [NO2Cl]2/[NO2]2[Cl2]
D)
K = [NO2]2[Cl2]/[NO2Cl]2
E)
K = [NO2Cl]2[NO2]2[Cl2]
11. At a given temperature, K = 0.017 for the equilibrium:
PCl5(g) PCl3(g) + Cl2(g)
What is K for:
Cl2(g) + PCl3(g) PCl5(g)?
A)
0.017
B)
59
C)
0.00029
D)
17
E)
3500
12. Given the equilibrium constants for the following reactions:
4Cu(s) + O2(g) 2Cu2O(s), K1
2CuO(s) Cu2O(s) + O2(g), K2
what is K for the system
2Cu(s) + O2(g) 2CuO(s)
equivalent to?
A)
(K1)(K2)
B)
C)
D)
E)
13. Which expression correctly describes the equilibrium constant for the following reaction?
4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)
A)
K = ( 4NH3] + 5[O2] ) / ( 4[NO] + 6[H2O] )
B)
K = ( 4[NO] + 6[H2O] ) / (4NH3] + 5[O2] )
C)
K = ( [NO][H2O] ) / ( [NH3][O2] )
D)
K = ( [NO]4[H2O]6 ) / ( [[NH3]4[O2]5 )
E)
K = ( [NH3]4[O2]5 ) / ( [NO]4[H2O]6 )
Consider the chemical system CO + Cl2 COCl2; K = 4.6 109 L/mol.
14. How do the equilibrium concentrations of the reactants compare to the equilibrium
concentration of the product?
A)
They are much smaller.
B)
They are much bigger.
C)
They are about the same.
D)
They have to be exactly equal.
E)
You can't tell from the information given.
1
2
15. If the concentration of the product were to double, what would happen to the equilibrium
constant?
A)
It would double its value.
B)
It would become half its current value.
C)
It would quadruple its value.
D)
It would not change its value.
E)
It would depend on the initial conditions of the product.
16. Determine the equilibrium constant for the system N2O4 2NO2 at 25°C. The
concentrations are shown here: [N2O4] = 2.32 10–2 M, [NO2] = 1.41 10–2 M.
A)
0.608
B)
1.65
C)
1.17 102
D)
0.369
E)
8.57 10–3
17. If K = 0.144 for A2 + 2B 2AB, then for 4AB 2A2 + 4B, K would equal:
A)
0.288
B)
0.144
C)
–0.144
D)
3.47
E)
48.2
18. Consider the gaseous reaction CO(g) + Cl2(g) COCl2(g). What is the expression for Kp
in terms of K?
A)
K(RT)
B)
K/(RT)
C)
K(RT)2
D)
K/(RT)2
E)
1/K(RT)
19. For the reaction N2O4(g) 2NO2(g), Kp = 0.148 at a temperature of 298 K. What is Kp
for the following reaction?
10NO2(g) 5N2O4(g)
A)
6.76
B)
0.74
C)
1.35
D)
1.41 104
E)
7.10 10–5
20. For the reaction H2(g) + Cl2(g) 2HCl(g), Kc = 1.22 1033 at a temperature of 301 K.
What is Kp at this temperature?
A)
1.22 1033
B)
3.01 1034
C)
4.93 1031
D)
7.43 1035
E)
2.00 1030
21. For the reaction NO(g) + O2(g) NO2(g) at 750°C, the equilibrium constant Kc equals:
A)
1.0
B)
Kp
C)
D)
E)
22. An equilibrium reaction, A2(g) + 3B2(g) 2C(g), has a Kp at 225°C of 2.6 10–3 /atm2.
What is K for this reaction at that temperature?
A)
1.6 10–6
B)
7.6 10–6
C)
4.3
D)
6.4 10–5
E)
0.89
1
2
23. Find the value of the equilibrium constant (K) (at 500 K) for N2(g) + 3H2(g) 2NH3(g).
The value for Kp at 500 K is 1.5 10–5/atm2.
A)
7.5 10–2
B)
1.3 10–2
C)
9.6 10–2
D)
2.5 10–2
E)
6.0 10–2
24. Consider the following reaction: CS2(g) + 4H2(g) CH4(g) + 2H2S(g). The equilibrium
constant K is about 0.31 at 900.°C. What is Kp at this temperature?
A)
2.9 103
B)
3.2 10–3
C)
3.3 10–5
D)
3.0 101
E)
1.1 10–3
25. Given the equation 2NOCl2(g) 2NO(g) + Cl2(g), the equilibrium constant is about
0.0196 at 115°C. Calculate Kp.
A)
0.0196
B)
0.624
C)
0.185
D)
19.9
E)
none of these
26. Calculate Kp for using the following data:
Kp = 2.3 106
Kp = 1.8 1037
A)
4.1 1043
B)
2.1 1043
C)
2.9 10–25
D)
5.4 10–13
E)
9.8 10–13
27. Consider the reaction:
CaCl2(s) + 2H2O(g) CaCl2·2H2O(s)
The equilibrium constant for the reaction as written is:
A)
K =
B)
C)
D)
K = [H2O]2
E)
K =
28. Consider the reaction At 1273 K, the Kp value is 167.5. What is
the at equilibrium if the is 0.17 atm at this temperature?
A)
2.7 atm
B)
0.085 atm
C)
11 atm
D)
5.3 atm
E)
7.5 atm
Consider the following equilibrium: H2(g) + I2(s) 2HI(g)
29. The proper Keq expression is:
A)
B)
C)
D)
E)
30. Which of the following statements about the equilibrium is false?
A)
If the system is heated, the right side is favored.
B)
This is a heterogeneous equilibrium.
C)
If the pressure on the system is increased by changing the volume, the left side is
favored.
D)
Adding more H2(g) increases the equilibrium constant.
E)
Removing HI as it forms forces the equilibrium to the right.
31. Consider the reaction: 2SO2(g) + O2(g) 2SO3(g) at constant temperature. Initially a
container is filled with pure SO3(g) at a pressure of 2 atm, after which equilibrium is
reached. If y is the partial pressure of O2 at equilibrium, the value of Kp is:
A)
B)
C)
D)
E)
none of these
32. Which of the following is true for a system whose equilibrium constant is relatively small?
A)
It will take a short time to reach equilibrium.
B)
It will take a long time to reach equilibrium.
C)
The equilibrium lies to the left.
D)
The equilibrium lies to the right.
E)
Two of these.
33. The reaction quotient for a system is 7.2 102. If the equilibrium constant for the system is
36, what will happen as equilibrium is approached?
A)
There will be a net gain in product.
B)
There will be a net gain in reactant.
C)
There will be a net gain in both product and reactant.
D)
There will be no net gain in either product or reactant.
E)
The equilibrium constant will decrease until it equals the reaction quotient.
34. Consider the following reaction:
2HF(g) H2(g) + F2(g) (K = 1.00 10–2)
Given 1.00 mole of HF(g), 0.362 mole of H2(g), and 0.750 mole of F2(g) are mixed in a
5.00 L flask, determine the reaction quotient, Q.
A)
Q = 0.0543
B)
Q = 0.272
C)
Q = 0.0679
D)
Q = 2.11
E)
none of these
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.
35. Predict the direction in which the system will move to reach equilibrium at 2000°C if 0.4
moles of N2, 0.1 moles of O2, and 0.08 moles of NO are placed in a 1.0-liter container.
A)
The system remains unchanged.
B)
The concentration of NO will decrease; the concentrations of N2 and O2 will
increase.
C)
The concentration of NO will increase; the concentrations of N2 and O2 will
decrease.
D)
The concentration of NO will decrease; the concentrations of N2 and O2 will
remain unchanged.
E)
More information is necessary.
36. A 1-L container originally holds 0.4 mol of N2, 0.1 mol of O2, and 0.08 mole 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 concentration of NO will increase; the concentrations of N2 and O2 will
decrease.
B)
The concentrations of N2 and O2 will increase; and the concentration of NO will
decrease.
C)
The concentrations of N2, O2, and NO will increase.
D)
The concentrations of N2, O2, and NO will decrease.
E)
There will be no change in the concentrations of N2, O2, and NO.
37. Consider the following equilibrated system: 2NO2(g) 2NO(g) + O2(g). If the Kp value
is 0.604, find the equilibrium pressure of the O2 gas if the NO2 gas pressure is 0.520 atm and
the PNO is 0.300 atm at equilibrium.
A)
1.05 atm
B)
24.8 atm
C)
0.348 atm
D)
0.201 atm
E)
1.81 atm
38. For the reaction given below, 2.00 moles of A and 3.00 moles of B are placed in a 6.00-L
container.
A(g) + 2B(g) C(g)
At equilibrium, the concentration of A is 0.213 mol/L. What is the value of K?
A)
2.18
B)
1.79
C)
0.213
D)
8.40
E)
0.565
39. A 10.0-g sample of solid NH4Cl is heated in a 5.00-L container to 900.°C. At equilibrium
the pressure of NH3(g) is 1.51 atm.
NH4Cl(s) NH3(g) + HCl(g)
The equilibrium constant, Kp, for the reaction is:
A)
1.51
B)
2.28
C)
3.02
D)
8.21
E)
none of these
40. Consider the reaction H2 + I2 2HI for which K = 44.8 at a high temperature. If an
equimolar mixture of reactants gives the concentration of the product to be 0.50 M at
equilibrium, determine the equilibrium concentration of the hydrogen.
A)
1.1 10–1 M
B)
7.5 10–2 M
C)
3.7 10–2 M
D)
1.3 101 M
E)
5.6 10–3 M
41. Consider the equation A(aq) + 2B(aq) 3C(aq) + 2D(aq). In one experiment, 45.0 mL
of 0.050 M A is mixed with 25.0 mL 0.100 M B. At equilibrium the concentration of C is
0.0410 M. Calculate K.
A)
7.3
B)
0.34
C)
0.040
D)
0.14
E)
none of these
42. 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 4.00 atm and hydrogen gas at a partial pressure of
0.213 atm. What is the partial pressure of I2?
A)
0.213 atm
B)
0.409 atm
C)
1.64 atm
D)
10.9 atm
E)
75.1 atm
43. For the equilibrium system:
CO2(g) + H2(g) CO(g) + H2O(g) H = +42 kJ/mol
K equals 1.6 at 1260 K. If 0.15 mol each of CO2, H2, CO, and H2O (all at 1260 K) were
placed in a 1.0-L thermally insulated vessel that was also at 1260 K, then as the system
came to equilibrium:
A)
The temperature would decrease and the mass of CO2 would increase.
B)
The temperature would decrease and the mass of CO2 would decrease.
C)
The temperature would remain constant and the mass of CO2 would increase.
D)
The temperature would increase and the mass of CO2 would increase.
E)
The temperature would increase and the mass of CO2 would decrease.
44. CS2(g) + 3Cl2(g) CCl4(g) + S2Cl2(g)
At a given temperature, the reaction above is at equilibrium when [CS2] = 0.050 M,
[Cl2] = 0.25 M, [CCl4] = 0.15 M, and [S2Cl2] = 0.35 M. What would be the direction of the
reaction when the reactants and products have the following concentrations: CS2 = 0.15 M,
Cl2 = 0.18 M, CCl4 = 0.29 M, and S2Cl2 = 0.21 M?
A)
to the right
B)
to the left
C)
no change
D)
cannot predict unless we know the temperature
E)
cannot predict unless we know whether the reaction is endothermic or exothermic
45. A mixture of nitrogen and hydrogen was allowed to come to equilibrium at a given
temperature.
3H2 + N2 2NH3
An analysis of the mixture at equilibrium revealed 2.1 mol N2, 3.2 mol H2, and 1.8 mol
NH3. How many moles of H2 were present at the beginning of the reaction?
A)
3.2
B)
4.8
C)
5.0
D)
5.9
E)
4.4
46. Carbon disulfide and chlorine react according to the following equation:
CS2(g) + 3Cl2(g) S2Cl2(g) + CCl4(g)
When 2.14 mol of CS2 and 5.85 mol of Cl2 are placed in a 2.00-L container and allowed to
come to equilibrium, the mixture is found to contain 0.620 mol of CCl4. How many moles
of Cl2 are present at equilibrium?
A)
1.520 mol
B)
0.620 mol
C)
3.99 mol
D)
4.61 mol
E)
2.00 mol
