Chapter 17: Equilibrium: The Extent of Chemical
Reactions
1. An equilibrium is established in which both the forward (fwd) and the reverse (rev)
reactions are elementary. If the equilibrium constant Kc = 1.6 × 10-2 and the rate constant kfwd =
8.0 × 10–7 s-1 what is the value of krev?
A) 1.3 × 10-8 s-1 D) 5.0 × 10-5 s-1
B) 7.8 × 107 s-1 E) none of the above
C) 2 × 104 s-1
2. Consider the equilibrium reaction shown below.
B2(g) 2B(g)
If the rate constants are: kfwd = 7.00 × 10-5 s-1 and krev = 2.00 × 10-5 L mol-1 s-1, what is the value
of Kc under these conditions?
A) 1.75 × 105 B) 3.50 C) 0.286 D) 5.71 × 10-6 E) 1.40 × 10–10
3. When a chemical system is at equilibrium,
A) the concentrations of the reactants are equal to the concentrations of the products.
B) the concentrations of the reactants and products have reached constant values.
C) the forward and reverse reactions have stopped.
D) the reaction quotient, Q, has reached a maximum.
E) the reaction quotient, Q, has reached a minimum.
4. A chemical reaction has an equilibrium constant of 2 × 106. If this reaction is at
equilibrium, select the one correct conclusion that can be made about the reaction.
A) The forward and back reactions have stopped.
B) The limiting reactant has been used up.
C) The forward and reverse rate constants are equal.
D) The forward and reverse reaction rates are equal.
E) None of the above conclusions is correct.
5. Which of the following has an effect on the magnitude of the equilibrium constant?
A) removing products as they are formed
B) adding more of a reactant
C) adding a catalyst
D) increasing the pressure, in a gas-phase reaction
E) change in temperature
Chapter 17: Equilibrium: The Extent of Chemical Reactions
6. In order to write the correct mass-action expression for a reaction one must
A) know the kinetic rate law for the reaction.
B) know the mechanism for the reaction.
C) have a properly balanced chemical equation.
D) have values for the concentrations of the reactants.
E) know the limiting reactant.
7. The two equilibrium constants for the same reaction, Kc and Kp, will always equal one
another when
A) all of the reactants and products are gases.
B) in the reaction equation, the number of moles of gaseous products equals the
number of moles of gaseous reactants.
C) in the reaction equation, the number of moles of gaseous products is greater than
the number of moles of gaseous reactants.
D) in the reaction equation, the number of moles of gaseous products is smaller than
the number of moles of gaseous reactants.
E) in the reaction equation, the total number of moles of reactants equals that of the
products.
8. The reaction quotient for a gas phase reaction has a value of 2000. If the number of
moles of reactants in the reaction equation is equal to that of the products, which of the
following statements is definitely true?
A) The reaction must proceed to the left to establish equilibrium.
B) The reaction must proceed to the right to establish equilibrium.
C) When the system is at equilibrium, the concentrations of the products will be much
larger than the concentrations of the reactants.
D) The concentrations of the products are generally larger than the concentrations of
the reactants.
E) None of the above statements is true.
9. The reaction quotient, Qc, for a reaction has a value of 75 while the equilibrium constant,
Kc, has a value of 195. Which of the following statements is accurate?
A) The reaction must proceed to the left to establish equilibrium.
B) The reaction must proceed to the right to establish equilibrium.
C) The concentrations of the products will be much smaller than the concentrations of
the reactants when the system is at equilibrium.
D) The concentrations of the products will be about the same as the concentrations of
the reactants when the system is at equilibrium.
E) None of the above statements is accurate.
Chapter 17: Equilibrium: The Extent of Chemical Reactions
10. Carbon monoxide and chlorine combine in an equilibrium reaction to produce the highly
toxic product, phosgene (COCl2)
CO(g) + Cl2(g) COCl2(g)
If the equilibrium constant for this reaction is Kc = 248, predict, if possible, what will happen
when the reactants and product are combined with the concentrations shown.
[CO] = [Cl2] = 0.010 M; [COCl2] = 0.070 M
A) The reaction will proceed to the right.
B) The reaction will proceed to the left.
C) The reaction is at equilibrium, and no change in concentrations will occur.
D) The container volume needs to be specified before a prediction can be made.
E) The temperature needs to be specified before a prediction can be made.
11. Carbon monoxide and chlorine combine in an equilibrium reaction to produce the highly
toxic product, phosgene (COCl2)
CO(g) + Cl2(g) COCl2(g)
If the equilibrium constant for this reaction is Kc = 248, predict, if possible, what will happen
when the reactants and product are combined with the concentrations shown.
[CO] = [Cl2] = 0.0200 M; [COCl2] = 0.0992 M
A) The reaction will proceed to the right.
B) The reaction will proceed to the left.
C) The reaction is at equilibrium, and no change in concentrations will occur.
D) The container volume needs to be specified before a prediction can be made.
E) The temperature needs to be specified before a prediction can be made.
12. Write the mass-action expression, Qc, for the following chemical reaction equation.
2C6H6(g) + 15O2(g) 12CO2(g) + 6H2O(g)
A)
 
 
22
6 6 2
CO H O
C H O
D)
 
 
2 15
6 6 2
12 6
22
C H O
CO H O
B)
 
 
12 6
22
2 15
6 6 2
CO H O
C H O
E)
 
 
22
6 6 2
12CO 6H O
2C H 15O
C)
 
 
6 6 2
22
C H O
CO H O
Chapter 17: Equilibrium: The Extent of Chemical Reactions
13. What is the mass-action expression, Qp, for the following reaction?
SbF5(g) + 4Cl2(g) SbCl3(g) + 5ClF(g)
A)
25
3
Cl SbF
SbCl ClF
( )( )
( )( )
PP
PP
B)
25
3
4
Cl SbF
5
SbCl ClF
( ) ( )
( )( )
PP
PP
C)
3
25
SbCl ClF
Cl SbF
( )( )
( )( )
PP
PP
D)
3
25
5
SbCl ClF
4
Cl SbF
( )( )
( ) ( )
PP
PP
E) None of the above is the correct mass-action expression.
14. Write the mass-action expression, Qc, for the following chemical reaction.
NO(g) +
12
Br2(g) NOBr(g)
A)
D)
B)
2
[NOBr]
[NO]0.5[Br ]
E)
0.5
2
[NOBr]
[NO][Br ]
C)
0.5
2
[NO][Br ]
[NOBr]
15. Write the mass-action expression, Qc , for the following chemical reaction.
3ClO2–(aq) 2ClO3–(aq) + Cl–(aq)
A)
2
3
3
2
[ClO ] ]Cl ]
[ClO ]
−−
−
D)
2
3
3[ClO ]
2[ClO ][Cl ]
−
−−
B)
3
2
2[ClO ][Cl ]
3[ClO ]
−−
−
E)
3
2
[2ClO ][Cl ]
[3ClO ]
−−
−
C)
3
2
2
3
[ClO ]
[ClO ] [Cl ]
−
−−
Chapter 17: Equilibrium: The Extent of Chemical Reactions
16. What is the mass-action expression, Qc , for the following chemical reaction?
Cu2+(aq) + 4NH3(aq) Cu(NH3)42+(aq)
A)
2
34
2
3
[Cu(NH ) ]
[Cu ] [NH ]
+
+
B)
2
34
24
3
[Cu(NH ) ]
[Cu ] [NH ]
+
+
C)
2
3
2
34
[Cu ] [NH ]
[Cu(NH ) ]
+
+
D)
24
3
2
34
[Cu ] [NH ]
[Cu(NH ) ]
+
+
E) None of the above is the correct mass-action expression.
17. Write the mass-action expression, Qc , for the following chemical reaction.
2Cu2+(aq) + 4I–(aq) 2CuI(s) + I2(aq)
A)
2
2
2 2 4
[CuI] [I ]
[Cu ] [I ]
+−
D)
2 2 4
2
[Cu ] [I ]
[I ]
+−
B)
2 2 4
2
2
[Cu ] [I ]
[CuI] [I ]
+−
E)
2
2
[2CuI] [I ]
[2Cu ] [4I ]
+−
C)
2
2 2 4
[I ]
[Cu ] [I ]
+−
18. Write the mass-action expression, Qc , for the following chemical reaction.
Zn(s) + 2Ag+(aq) Zn2+(aq) + 2Ag(s)
A)
22
2
[Zn ] [Ag( )]
[Zn( )] [Ag ]
s
s
+
+
D)
2
2
[Ag ]
[Zn ]
+
+
B)
2
22
[Zn( )] [Ag ]
[Zn ] [Ag( )]
s
s
+
+
E)
2
2
[Zn ]
[Ag ]
+
+
C)
2
[Zn ]
[Ag ]
+
+
Chapter 17: Equilibrium: The Extent of Chemical Reactions
19. Write the mass-action expression, Qc , for the following chemical reaction.
Fe3+(aq) + 3OH–(aq) Fe(OH)3(s)
A)
3
33
[Fe(OH) ]
[Fe ] [OH ]
+−
D)
33
[Fe ] [OH ]
+−
B)
33
3
[Fe ] [OH ]
[Fe(OH) ]
+−
E)
3
1
[Fe ]3 [OH ]
+−
C)
33
1
[Fe ] [OH ]
+−
20. What is the mass-action expression, Qc , for the following chemical reaction?
PbO(s) + CO(g) Pb(l) + CO2(g)
A)
2
[CO ]
[CO]
B)
2
[CO]
[CO ]
C)
2
[Pb] [CO ]
[PbO] [CO]
D)
2
[Pb] [CO ]
[CO]
E) None of the above expressions is correct.
21. What is the mass-action expression, Qc , for the following chemical reaction?
4H3O+(aq) + 2Cl–(aq) + MnO2(s) Mn2+(aq) + 6H2O(l) + Cl2(g)
A)
42
32
26
22
[H O ] [Cl ] [MnO ]
[Mn ] [H O] [Cl ]
+−
+
B)
26
22
42
32
[Mn ] [H O] [Cl ]
[H O ] [Cl ] [MnO ]
+
+−
C)
42
3
2
2
[H O ] [Cl ]
[Mn ] [Cl ]
+−
+
D)
2
2
42
3
[Mn ] [Cl ]
[H O ] [Cl ]
+
+−
E) None of the above expressions is correct.
Chapter 17: Equilibrium: The Extent of Chemical Reactions
22. Write the mass-action expression, Qc , for the following chemical reaction.
MgO(s) + SO2(g) +
12
O2(g) MgSO4(s)
A)
1/2
22
4
[MgO] [SO ][O ]
[MgSO ]
B)
4
1/2
22
[MgSO ]
[MgO] [SO ][O ]
C)
1/2
22
1
[SO ][O ]
D)
1/2
22
[SO ][O ]
E) None of the above expressions is correct.
23. Write the mass-action expression, Qc , for the following chemical reaction.
Sn2+(aq) +
12
O2(g) + 3H2O(l) SnO2(s) + 2H3O+(aq)
A)
2
3
2 1/2
2
[H O ]
[Sn ][O ]
+
+
B)
2 1/2
2
2
3
[Sn ][O ]
[H O ]
+
+
C)
2
23
2 1/2
22
[SnO ][H O ]
[H O][Sn ][O ]
+
+
D)
2
3
2 1/2
22
[H O ]
[H O][Sn ][O ]
+
+
E) None of the above expressions is correct.
24. Consider the reactions of cadmium with the thiosulfate anion.
Cd2+(aq) + S2O32–(aq) Cd(S2O3)(aq) K1 = 8.3 × 103
Cd(S2O3)(aq) + S2O32–(aq) Cd(S2O3)22–(aq) K2 = 2.5 × 102
What is the value for the equilibrium constant for the following reaction?
Cd2+(aq) + 2S2O32–(aq) Cd(S2O3)22–(aq)
A) 0.030 B) 33 C) 8.1 × 103 D) 8.6 × 103 E) 2.1 × 106
Chapter 17: Equilibrium: The Extent of Chemical Reactions
25. N2(g) + O2(g) 2NO(g) Kc = 4.8 × 10–31
2NOBr(g) 2NO(g) + Br2(g) Kc = 0.50
Given the above equilibrium constant data at 25 °C, what is the value of Kc at this temperature
for the reaction
2NOBr(g) N2(g) + O2(g) + Br2(g)?
A) 2.4 × 10–31 D) 4.2 × 1030
B) 9.6 × 10–31 E) none of the above
C) 1.0 × 1030
26. H2SO3(aq) HSO3–(aq) + H+(aq) Kc = 1.4 × 10-2
H2SO3(aq) SO32-(aq) + 2H+(aq) Kc = 9.1 × 10–10
Given the above equilibrium constant data at 25 °C, what is the value of Kc at this temperature
for the reaction
HSO3–(aq) SO32-(aq) + H+(aq)?
A) 6.5 × 10-8 D) 1.5 × 107
B) 1.3 × 10–11 E) none of the above
C) 7.8 × 1010
27. Hydrogen sulfide will react with water as shown in the following reactions.
H2S(g) + H2O(l) H3O+(aq) + HS–(aq) K1 = 1.0 × 10–7
HS–(aq) + H2O(l) H3O+(aq) + S2–(aq) K2 = ?
H2S(g) + 2H2O(l) 2H3O+(aq) + S2–(aq) K3 = 1.3 × 10–20
What is the value of K2?
A) 1.3 × 10–27
B) 2.3 × 10–7
C) 1.3 × 10–13
D) 7.7 × 1012
E) 7.7 × 1026
28. At 500°C the equilibrium constant, Kp , is 4.00 × 10–4 for the equilibrium:
2HCN(g) H2(g) + C2N2(g)
What is Kp for the following reaction?
H2(g) + C2N2(g) 2HCN(g)
A) 2.00 × 10–4 D) 2.50 × 103
B) –4.00 × 10–4 E) 4.00 × 104
C) 1.25 × 103
Chapter 17: Equilibrium: The Extent of Chemical Reactions
29. About half of the sodium carbonate produced is used in making glass products because it
lowers the melting point of sand, the major component of glass. When sodium carbonate is
added to water it hydrolyses according to the following reactions.
CO32–(aq) + H2O(l) HCO3–(aq) + OH–(aq) K1
HCO3–(aq) + H2O(l) H2CO3(aq) + OH–(aq) K2
These can be combined to yield
CO32–(aq) + 2H2O(l) H2CO3(aq) + 2OH–(aq) K3
What is the value of K3?
A) K1 × K 2 B) K1 ÷ K 2 C) K 1 + K 2 D) K 1 – K 2 E) (K1K2)2
30. The equilibrium constant, Kc , for the decomposition of COBr2
COBr2(g) CO(g) + Br2(g)
is 0.190. What is Kc for the following reaction?
2CO(g) + 2Br2(g) 2COBr2(g)
A) 0.0361 B) 2.63 C) 5.62 D) 10.5 E) 27.7
31. The equilibrium constant for the reaction of bromine with chlorine to form bromine
monochloride is 58.0 at a certain temperature.
Br2(g) + Cl2(g) 2BrCl(g)
What is the equilibrium constant for the following reaction?
BrCl(g)
12
Br2(g) +
12
Cl2(g)
A) 2.97 × 10–4
B) 1.72 × 10–2
C) 3.45 × 10–2
D) 1.31 × 10–1
E) > 1.00
32. Consider the following two equilibria and their respective equilibrium constants:
(1) NO(g) +
12
O2(g) NO2(g)
(2) 2NO2(g) 2NO(g) + O2(g)
Which one of the following is the correct relationship between the equilibrium constants K1 and
K2?
A) K2 = 2/K1 D) K2 = 1/(2K1)
B) K2 = (1/K1)2 E) K2 = 1/(2K1)2
C) K2 = –K1/2
Chapter 17: Equilibrium: The Extent of Chemical Reactions
33. The equilibrium constant for reaction (1) below is 276. Under the same conditions, what
is the equilibrium constant of reaction (2)?
(1)
12
X2(g) +
12
Y2(g) XY(g)
(2) 2XY(g) X2(g) + Y2(g)
A) 6.02 × 10–2 D) 1.31 × 10–5
B) 7.25 × 10–3 E) none of the above
C) 3.62 × 10–3
34. In water, the following equilibrium exists:
H+(aq) + OH–(aq) H2O(l)
In pure water at 25 °C, the concentration of H+ ions is 1.00 × 10-7 mol/L. Calculate the value of
the equilibrium constant for the reaction as written above.
A) 1.00 × 1014 D) 1.00 × 10–12
B) 1.00 × 1012 E) 5.55 × 1015
C) 1.00 × 10–14
35. Consider the equilibrium reaction: N2O4(g) 2NO2(g)
Which of the following correctly describes the relationship between Kc and Kp for the reaction?
A) Kp = Kc D) Kp = Kc /RT
B) Kp = RT × Kc E) Kp = RT/Kc
C) Kp = (RT × Kc)–1
36. Consider the equilibrium reaction: H2(g) + Br2(g) 2HBr(g)
Which of the following correctly describes the relationship between Kc and Kp for the reaction?
A) Kp = Kc D) Kp = Kc/RT
B) Kp = (RT)Kc E) Kp = Kc/(RT)2
C) Kp = (RT)2Kc
37. The equilibrium constant, Kp, has a value of 6.5 × 10–4 at 308 K for the reaction of
nitrogen monoxide with chlorine.
2NO(g) + Cl2(g) 2NOCl(g)
What is the value of Kc?
A) 2.5 × 10–7
B) 6.5 × 10–4
C) 1.6 × 10–2
D) 1.7
E) none of the above
Chapter 17: Equilibrium: The Extent of Chemical Reactions
38. The reaction of nitrogen with oxygen to form nitrogen monoxide can be represented by
the following equation.
N2(g) + O2(g) 2NO(g)
At 2000°C, the equilibrium constant, Kc , has a value of 4.10 × 10–4. What is the value of Kp?
A) 2.17 × 10–8 D) 7.75
B) 4.10 × 10–4 E) none of the above
C) 7.65 × 10–2
39. Nitrogen dioxide decomposes according to the reaction
2NO2(g) 2NO(g) + O2(g)
where Kp = 4.48 × 10–13 at 25°C. What is the value for Kc?
A) 1.81 × 10–16 D) 1.10 × 10–11
B) 1.83 × 10–14 E) 1.11 × 10–9
C) 4.48 × 10–13
40. The equilibrium constant, Kp , for the reaction
H2(g) + I2(g) 2HI(g)
is 55.2 at 425°C. A rigid cylinder at that temperature contains 0.127 atm of hydrogen, 0.134 atm
of iodine, and 1.055 atm of hydrogen iodide. Is the system at equilibrium?
A) Yes.
B) No, the forward reaction must proceed to establish equilibrium.
C) No, the reverse reaction must proceed to establish equilibrium.
D) Need to know the volume of the container before deciding.
E) Need to know the starting concentrations of all substances before deciding.
41. The equilibrium constant, Kp , for the reaction
CO(g) + H2O(g) CO2(g) + H2(g)
at 986°C is 0.63. A rigid cylinder at that temperature contains 1.2 atm of carbon monoxide, 0.20
atm of water vapor, 0.30 atm of carbon dioxide, and 0.27 atm of hydrogen. Is the system at
equilibrium?
A) Yes.
B) No, the forward reaction must proceed to establish equilibrium.
C) No, the reverse reaction must proceed to establish equilibrium.
D) Need to know the volume of the container before deciding.
E) Need to know the starting concentrations of all substances before deciding.
Chapter 17: Equilibrium: The Extent of Chemical Reactions
42. Nitric oxide and bromine were allowed to react in a sealed container. When equilibrium
was reached PNO = 0.526 atm,
2
Br
P
= 1.59 atm, and PNOBr = 7.68 atm. Calculate Kp for the
reaction.
2NO(g) + Br2(g) 2NOBr(g)
A) 7.45 × 10–3 B) 0.109 C) 9.18 D) 91.8 E) 134
43. Compounds A, B, and C react according to the following equation.
3A(g) + 2B(g) 2C(g)
At 100°C a mixture of these gases at equilibrium showed that [A] = 0.855 M, [B] = 1.23 M, and
[C] = 1.75 M. What is the value of Kc for this reaction?
A) 0.309 B) 0.601 C) 1.66 D) 3.24 E) > 10
44. Consider the reversible reaction: 2NO2(g) N2O4(g)
If the concentrations of both NO2 and N2O4 are 0.016 mol L–1, what is the value of Qc?
A) 0.016 B) 0.50 C) 1.0 D) 2.0 E) 63
45. 10.0 mL of a 0.100 mol L–1 solution of a metal ion M2+ is mixed with 10.0 mL of a 0.100
mol l–1 solution of a substance L. The following equilibrium is established:
M2+(aq) + 2L(aq) ML22+(aq)
At equilibrium the concentration of L is found to be 0.0100 mol L–1. What is the equilibrium
concentration of ML22+, in mol L–1?
A) 0.100 mol L–1 D) 0.0200 mol L–1
B) 0.050 mol L–1 E) 0.0100 mol L–1
C) 0.025 mol L–1
46. Hydrogen iodide, HI, is formed in an equilibrium reaction when gaseous hydrogen and
iodine gas are heated together. If 20.0 g of hydrogen and 20.0 g of iodine are heated, forming
10.0 g of hydrogen iodide, what mass of hydrogen remains unreacted?
A) 10.0 g hydrogen remains
B) 10.9 g hydrogen remains
C) 15.0 g hydrogen remains
D) 19.9 g hydrogen remains
E) Need to know the equilibrium constant in order to calculate the answer.
47. SO2 reacts with O2 to produce SO3. If 86.0 g of SO2 is placed in a reaction vessel along
with excess oxygen gas, how many moles of SO2 remain when 50.0 g of SO3 have been formed?
A) 0.56 mol B) 0.62 mol C) 0.72 mol D) 0.78 mol E) 1.34 mol