102 Sample Test 1
CHAPTER 14
Chapter 14. Chemical Equilibrium
1. The equilibrium expression for Kc for the system
CO2 (g) + CaO <====> CaCO3 (s) is
a. [CaCO3]
[CO2][CaO]
b. [CaCO3]
[CO2]
c. [CaCO3]
[CO2][CaO]
d. 1
[CO2]
e. CO2
2. The equilibrium constant expression, Kc, for the reaction
C3H8(g) + 5O2(g) <==> 3CO2(g) + 4H2O(g).
[C3H8][O2]5
a. Kc= ———————
[CO2]3[H2O]4
b. Kc= [CO2]3[H2O]4
[CO2]3[H2O]4
c. Kc= ———————
[C3H8][O2]5
d. Kc= [C3H8][O2]5
[C3H8][O2]3
e. Kc= ————————
[CO2]5[H2O]4
3. Chemical equilibrium
a. is a dynamic equilibrium.
b. describes opposing chemical reactions.
c. involves changes that occur at equal rates.
d. is described by each of these statements.
4. Chemical equilibrium exists when
a. reactants are completely changed to products.
b. there are equal amounts of reactants and products.
c. the rate at which reactants form products becomes zero.
d. the rate at which reactants form products is the same as the rate at which products form reactants.
5. Homogeneous equilibria are those that involve
a. only chemical changes.
b. only one phase.
c. static, not dynamic, equilibria.
d. a single reactant.
6. The term initial concentration refers to the
a. first concentration listed in the problem.
b. concentration of the first reactant in the equation.
c. concentrations at the start of the experiment.
d. amount of product formed by the first reaction of a series.
7. Which of the following correctly describes the equilibrium constant for the gas-phase reaction between H2 and O2
to form gaseous H2O?
2H2(g) + O2(g) <====> 2H2O(g)
[H2O]2
a. Kc = -------[H2][O2]
[H2O]
b. Kc = -------[H2]2[O2]
[H2O]2
c. Kc = -------[H2]2[O2]
[H2][O2]
d. Kc = -------[H2O]
e. Kc = [H2O]
8. For the reaction, 5CO(g) + I2O5(s) <----> I2(g) + 5CO2(g)
the expression for Kc is
a. [CO]5[I2O5]
[I2][CO2]5
b. [I2][CO2]5
[CO]5
c. [I2][CO2]5
[CO]5[I2O5]
d. [I2][CO2]
[CO]
9. The homogeneous equilibrium in this list is
a. Ag+(aq) + Cl-(aq) <==> AgCl(s).
b. P4O10(s) <==> P4(g) + 5O2(g).
c. HCl(g) + NH3(g) <==> NH4Cl(s).
d. PCl5(g) <==> PCl3(g) + Cl2(g).
10. If the reaction quotient (Q) for a reaction is greater than Kc then
a. the reaction must move to the right to reach equilibrium.
b. the reaction must move to the left to reach equilibrium.
c. the reaction is at equilibrium.
d. the temperature must rise to reach equilibrium.
11. For the reaction: 3H2(g) + N2(g) <===> 2NH3(g)
the relationship between K and Kp at a given temperature T is:
a. K = 1/Kp
b. K = Kp(RT)-2
c. Kp = K(RT)-2
d. K = Kp
e. none of these
12. Consider the equilibrium 3H2(g) + N2(g) <===> 2NH3(g) at a certain temperature. An equilibrium mixture in a
4.00-L vessel contains 1.60 mol NH3(g), 0.800 mol N2(g), and 1.20 mol H2(g). What is the value of Kc?
a. 9.00
b. 29.6
c. 3.37
d. 17.1
e. 7.41
13. Consider the reaction
S2Cl2(l) + CCl4(l) <===> CS2(g) + 3Cl2(g); ∆H = +84.3 kJ
If the above reactants and products are contained in a closed vessel and the reaction system is at equilibrium, the
number of moles of CS2(g) can be increased by
a. removing some S2Cl2(l) from the system.
b. removing some CCl4(l) from the system.
c. increasing the pressure of the reaction vessel.
d. increasing the temperature of the reaction system.
e. adding some Cl2(g) to the system.
14. Which of the following equilibria would not be affected by pressure changes at constant temperature?
a. FeO(s) + CO(g) <===> Fe(s) + CO2(g)
b. CaCO3(s) <===> CaO(s) + CO2(g)
c. 2H2O(g) <===> 2H2(g) + O2(g)
d. 2NO(g) + O2(g) <===> 2NO2(g)
e. PCl5(l) <===> PCl3(g) + Cl2(g)
15. According to La Chatelier's Principle, for the following reaction at equilibrium:
2NO(g) + Cl2(g) <===> 2ClNO(g)
If the pressure of the reaction container is decreased:
a. the number of ClNO molecules increases
b. the number of Cl2 molecules increases
c. the number of NO molecules decreases
d. the number of NO molecules stays constant
e. the number of Cl2 molecules decreases
16. Consider following system at equilibrium:
PCl5(g) <==> PCl3(g) + Cl2(g); ∆H = +500 kJ
Which of the following changes will shift the equilibrium to the LEFT?
a. increasing temperature
b. increasing volume
c. increasing pressure
d. removing Cl2(g)
e. adding PCl5(g)
17. A 1.00-mol sample of HI is placed in a 1-L vessel at 460oC, and the reaction system
is allowed to come to equilibrium. The HI partially decomposes, forming 0.11 mol H2
and 0.11 mol I2. What is the equilibrium constant for the reaction
H2(g) + I2(g) <===> 2HI(g)
at 460oC?
a. 0.020
b. 7.1
c. 8.1
d. 50.3
e. 30.1
18. For the reaction N2(g) + 3 H2(g) <+==> 2 NH3(g) an equilibrium mixture at 298 K in
a 4.00 L container has 1.60 mol of NH3, 0.800 mol of N2, and 1.20 of mol H2. The value of Kc is
a. 0.150.
b. 0.0338.
c. 29.6.
d. 6.67.
19. For the reaction Ni(s) + 4 CO(g) <=== Ni(CO)4(g), the equilibrium constant expression is
20. A weak acid is 5% ionized. Therefore we can say that this reaction is _____-favored, because _____.
a.
product; the amount of products >> the amount of reactants
b.
product; the amount of products << the amount of reactants
c.
reactant; the amount of products >> the amount of reactants
d.
reactant; the amount of products << the amount of reactants
e.
neither; not enough information is available to reach a conclusion
21. Two reactants are combined and the system eventually reaches equilibrium. Which statement about the rates
of the forward and reverse reactions is correct?
a.
From the beginning of the reaction until equilibrium, the rate of the forward reaction decreased and the rate of
reverse reaction increased.
b.
From the beginning of the reaction until equilibrium, the rate of the forward reaction and the rate of the reverse
reaction increased.
c.
From the beginning of the reaction until equilibrium, the rate of the forward reaction and the rate of the reverse
reaction decreased.
d.
From the beginning of the reaction until equilibrium, the rate of the forward reaction increased and the rate of
the reverse reaction decreased.
e.
From the beginning of the reaction until equilibrium, the rate of the forward reaction remained the same as the
rate of the reverse reaction.
22. Consider the reaction
4NH3(g) + 5O2(g) <===> 4NO(g) + 6 H2O(g)
The equilibrium constant expression for this reaction is
a.
4[NH 3 ]5[O 2 ]
K =
c 4[NO]6[H 2 O]
b.
4[NO]6[H 2 O]
K =
c 4[NH 3 ]5[O 2 ]
c.
[NH 3 ]4 [O 2 ]5
K =
c [NO]4 [H O]6
2
d.
e.
[NO]4 [H 2 O]6
K =
c [NH ]4 [O ]5
3
2
[NO][H 2 O]
K =
c [NH 3 ][O 2 ]
23. Consider the reaction
4NH3(g) + 5O2(g) <===> 4NO(g) + 6H2O(g)
The equilibrium constant expression for reverse of this reaction is
a.
4[NH 3 ]5[O 2 ]
Kc =
b.
c.
d.
e.
4[NO]6[H 2 O]
4[NO]6[H 2 O]
Kc =
4[NH 3 ]5[O 2 ]
Kc =
[NH 3 ]4 [O 2 ]5
[NO]4 [H 2 O]6
Kc =
[NO]4 [H 2 O]6
[NH 3 ]4 [O 2 ]5
Kc =
[NO][H 2 O]
[NH 3 ][O 2 ]
24. Consider the reaction
2 NOCl(g) <===> 2 NO(g) + Cl2(g)
If this reaction is multiplied through by 2 what would be the equilibrium constant expression?
a.
[ NO]2 [C12 ]
K =
c
[NOC1]2
b.
[ NO]2 [C12 ]
K =2
c
[NOC1] 2
c.
[ NO]4 [C12 ] 2
K =
c
[NOC1] 4
d.
[ NOC1]4
K =
c [NO]4 [C12 ] 2
e.
[ NOC1] 2
K =
c [NO]2 [C12 ]
25. Consider the reaction
Br2(g) + Cl2(g) <===> 2BrCl(g)
Calculate the value of Kp at 400°C if the partial pressures of BrCl, Br2, and Cl2 are 1.87 atm, 1.00 atm,
and 0.50 atm, respectively.
a.
7.0
b.
3.7
c.
2.3
d.
0.27
e.
0.14
26. Consider the reaction
Br2(g) + Cl2(g) <===> 2BrCl(g)
Calculate the value of Kp at 400°C if the partial pressures of BrCl, Br2, and Cl2 are 3.74 atm, 2.00 atm,
and 1.00 atm, respectively.
a.
0.14
b.
0.53
c.
1.9
d.
4.7
e.
7.0
27. Consider the reaction
COCl2(g) <===> CO(g) + Cl2(g)
At equilibrium, [CO] = 4.14 × 10-6 M; [Cl2] = 4.14 × 10-6 M; and [COCl2] = 0.0627 M. Calculate the
value of the equilibrium constant.
a.
1.32 × 10-4
b.
1.51 × 104
c.
2.73 × 10-10
d.
3.66 × 109
e.
6.60 × 10-5
28. Consider the reaction A <===> B, where the value of Kc is 1.4 × 1015. Which statement about the system at
equilibrium is correct?
a.
The amount of A is very close to the amount of B.
b.
The amount of A is slightly less than the amount of B.
c.
The amount of A is much larger than the amount of B.
d.
The amount of A is much less than the amount of B.
e.
More information is needed to make any statement about
relative amounts of the two chemicals.
29. Consider the reaction A <===> B, where the value of Kc is 1.4 × 10-12. Which statement about the system at
equilibrium is correct?
a.
The amount of A is very close to the amount of B.
b.
The amount of A is slightly less than the amount of B.
c.
The amount of A is much larger than the amount of B.
d.
The amount of A is much less than the amount of B.
e.
More information is needed to make any statement about the
amounts of the two chemicals.
30. Consider the reaction system
ethanol + acetic acid <====> ethyl acetate, where
Kc =
[ethyl acetate]
= 0.95
[ethanol][acetic acid]
The concentrations of ethanol and acetic acid are 0.45 M and the concentration of ethyl acetate is 1.1 M.
Use the reaction quotient to determine whether the system is at equilibrium.
a.
The value of Q is 5.43, and the system is at equilibrium.
b.
The value of Q is 2.4, and the system is at equilibrium.
c.
The value of Q is 0.95, and the system is at equilibrium.
d.
The value of Q is 5.43, and the system is not at equilibrium.
e.
The value of Q is 2.4, and the system is not at equilibrium.
31. Consider the reaction 2A <===> B, where the value of K is 1.4 × 1015. At equilibrium, the concentration of
A is 0.45 M. What is the concentration of B?
a.
0.90
b.
2.5 × 107
c.
2.8 × 1014
d.
6.3 × 1014
e.
1.1 × 1015
32. Consider the reaction A <===> 2B, where the value of K is 1.4 × 10-12. At equilibrium, the concentration of
B is 0.45 M. What is the concentration of A?
a.
2.8 × 10-13
b.
6.3 × 10-13
c.
1.4 × 1011
d.
3.2 × 1011
e.
5.8 × 1011
33. Consider the reaction 3A <===> 2B, where the value of K is 22.1. If the concentration of A is 0.015 at
equilibrium, what is the concentration of B?
a.
6.5 × 106
b.
1.0
c.
0.010
d.
8.6 × 10-3
e.
7.5 × 10-5
34. Consider the equilibrium system
C(s) + CO2(g) <====> 2CO(g)
If more carbon is added, the equilibrium will ____, and if CO is removed the equilibrium will ____.
a.
shift forward; shift reverse
b.
shift forward; shift forward
c.
shift reverse; shift reverse
d.
Be unchanged; shift forward
e.
neither can be predicted
35. Consider the equilibrium system
C(s) + CO2(g) <====> 2CO(g)
If CO2 is added, the equilibrium will ____, and if CO is added the equilibrium will ____.
a.
shift forward; shift reverse
b.
shift forward; shift forward
c.
shift reverse; shift reverse
d.
Be unchanged; shift forward
e.
neither can be predicted
36. Consider the equilibrium system
C(s) + CO2(g) <====> 2CO(g)
If C is removed, the equilibrium will ____, and if CO is added, the equilibrium will ____.
a.
shift forward; shift reverse
b.
shift forward; shift forward
c.
shift reverse; shift reverse
d.
Be unchanged; shift reverse
e.
neither can be predicted
37. Consider the equilibrium system
C(s) + CO2(g) <====> 2CO(g)
If the pressure on the system is increased the equilibrium will _____, because _____.
a.
shift forward; higher pressure favors fewer moles of gas
b.
shift forward; higher pressure favors more moles of gas
c.
shift reverse; higher pressure favors fewer moles of gas
d.
shift reverse; higher pressure favors more moles of gas
e.
Be unchanged; of the presence of the solid C
38. Consider the equilibrium system
C(s) + CO2(g) <====> 2CO(g)
If the pressure on the system is decreased the equilibrium will _____, because _____.
a.
shift forward; lower pressure favors fewer moles of gas
b.
shift forward; lower pressure favors more moles of gas
c.
shift reverse; lower pressure favors fewer moles of gas
d.
shift reverse; lower pressure favors more moles of gas
e.
Be unchanged; of the presence of the solid C
39. Consider the endothermic reaction at equilibrium:
C(s) + CO2(g) <====> 2CO(g)
If the system is heated, the equilibrium will _____, because _____.
a.
shift forward; increased temperature favors an endothermic reaction
b.
shift forward; increased temperature favors an exothermic reaction
c.
shift reverse; increased temperature favors an endothermic reaction
d.
shift reverse; increased temperature favors an exothermic reaction
e.
be unchanged; temperature has no effect on equilibrium
40. Consider the endothermic reaction at equilibrium:
C(s) + CO2(g) <====> 2CO(g)
If the system is cooled, the equilibrium will _____, because _____.
a.
shift forward; decreased temperature favors an endothermic reaction
b.
shift forward; decreased temperature favors an exothermic reaction
c.
shift reverse; decreased temperature favors an endothermic reaction
d.
shift reverse; decreased temperature favors an exothermic reaction
e.
be unchanged; temperature has no effect on equilibrium
41. At room temperature, if the value of Kc for a given reaction is a large number, we can conclude that the
energy of the products is likely to be _____ the energy of the reactants because _____.
a.
less than; the value of Kc favors the reactants
b.
less than; the value of Kc favors the products
c.
the same as; the value of Kc favors neither the products nor the reactants
d.
greater than; the value of Kc favors the reactants
e.
greater than; the value of Kc favors the products
42. At room temperature, if the value of Kc for a given reaction is a very small number, we can conclude that
the energy of the products is likely to be _____ the energy of the reactants because _____.
a.
less than; the value of Kc favors the reactants
b.
less than; the value of Kc favors the products
c.
the same as; the value of Kc favors neither the products nor the reactants
d.
greater than; the value of Kc favors the reactants
e.
greater than; the value of Kc favors the products
43. In predicting which state of an equilibrium is more favored, the factor concerned with probability is called
a.
enthalpy
b.
entropy
c.
molarity
d.
temperature
e.
work
44. Considering only the probability factor in the gaseous reaction 2A + B <===> C, the ____ side is favored
because ____.
a.
product; there are more possible arrangements of molecules on the reactant side
b.
product; there are more possible arrangements of molecules on the product side
c.
reactant; there are more possible arrangements of molecules on the reactant side
d.
reactant; there are more possible arrangements of molecules on the product side
e.
More information is needed to determine which side is favored.
45. Which factor concerning a reaction system most influences the relative importance of the probability factor
versus the energy factor?
a.
total number of moles
b.
volume
c.
density of any liquids
d.
temperature
e.
pressure
46. Consider the exothermic reaction for the manufacture of ammonia: N2(g) + 3H2(g) → 2NH3(g)
This reaction is ____-favored on the basis of enthalpy and ____-favored on the basis of entropy.
a.
product; product
b.
reactant; reactant
c.
product; reactant
d.
reactant; product
e.
More information is needed to make this determination.
47. Consider the exothermic reaction for the manufacture of ammonia: N2(g) + 3H2(g) → 2NH3(g). If the
pressure on this system is increased, the equilibrium will shift to the _____; if the temperature is increased the
equilibrium will shift to the _____.
a.
right; right
b.
left; left
c.
neither; left
d.
right; left
e.
left; right
Answer Key
1. Ans: d 1/[CO2]
[CO2]3[H2O]4
2. Ans: c
Kc= ———————
[C3H8][O2]5
3. Ans: d is described by each of these statements.
4. Ans: d the rate at which reactants form products is the same as the rate at which products form reactants.
5. Ans: b. only one phase.
6. Ans: c concentrations at the start of the experiment.
[H2O]2
7. Ans: c
Kc = -------[H2]2[O2]
8. Ans: b [I2][CO2]5
[CO]5
9. Ans: d PCl5(g) <==> PCl3(g) + Cl2(g).
10. Ans: b the reaction must move to the left to reach equilibrium.
11. Ans: c Kp = K(RT)-2
12. Ans: b 29.6
13. Ans: d increasing the temperature of the reaction system.
14. Ans: a FeO(s) + CO(g) <===> Fe(s) + CO2(g)
15. Ans: b the number of Cl2 molecules increases
16. Ans: c increasing pressure
17. Ans: d 50.3
18. Ans: c 29.6.
19. Ans: a
20. Ans: D. reactant; the amount of products << the amount of reactants
21. Ans:A. From the beginning of the reaction until equilibrium, the rate of the forward reaction
decreased and the rate of the reverse reaction increased.
22. Ans:: D
23. Ans: C
24. Ans: C
25. Ans: A. 7.0
26. Ans: E. 7.0
27. Ans: C. 2.73 × 10-10
28. Ans: D. The amount of A is much less than the amount of B.
29.Ans: C. The amount of A is much larger than the amount of B.
30. Ans: D. The value of Q is 5.43, and the system is not at equilibrium.
31. Ans: C. 2.8 × 1014
32. Ans: C. 1.4 × 1011
33. Ans: D. 8.6 × 10-3
34. Ans: D. be unchanged; shift forward
35. Ans: A. shift forward; shift reverse
36. Ans: D. be unchanged; shift reverse
37. Ans: C. shift reverse; higher pressure favors fewer moles of gas
38. Ans: B shift forward; lower pressure favors more moles of gas
39. Ans: A. shift forward; increased temperature favors an endothermic reaction
40. Ans: D. shift reverse; decreased temperature favors an exothermic reaction
41. Ans: B. less than; the value of Kc favors the products
42. Ans: D. greater than; the value of Kc favors the reactants
43. Ans: B. entropy
44. Ans: C. reactant; there are more possible arrangements of molecules on the reactant side
45. Ans: D. temperature
46. Ans: C. product; reactant
47. Ans: D. right; left