CHM 2046
Exam 1
January 27, 2005
Important: Bubble in A, B or C as the test form code at the top right of your answer sheet.
VERSION 0
For this version, the correct answer for each question is a.
1.
Once the reaction A + B ⇌ C + D reaches equilibrium, there is no net change to the
concentrations of the species involved in the reaction because:
a.
b.
c.
d.
the forward reaction rate is equal to the backward reaction rate.
the concentrations of A, B, C and D are all equal.
reactions in both directions have stopped and nothing further can happen.
one of the species has been completely consumed, and is thus no longer available
to react.
not possible to decide without Kc.
e.
2.
3.
If the equilibrium constant, K, for a reaction A ⇌ B is 1.0 x 105, which of the following is
true at equilibrium?
a.
b.
c.
d.
All of the other four statements are true.
The reaction lies far to the right-hand side.
The forward reaction rate is much greater than the backward reaction rate.
[B] >> [A]
e.
The K for B ⇌ A is 1.0 x 10-5.
Consider the reaction
N2O4 (g) ⇌ 2 NO2 (g)
At a particular moment in time, [N2O4] is found to be increased. Which of the following
statements is true?
a.
b.
c.
d.
e.
4.
Qc > Kc
Qc < Kc
Qc = Kc
Qc < 0
cannot decide without knowing Kc.
What is Qc for the following reaction?
2 CH4 (g) ⇌ C2H2 (g) + 3 H2 (g)
Qc 
[ H 2 ]3 [C2 H 2 ]
[CH 4 ]2
Qc 
[C2 H 2 ][ H 2 ]
[CH 4 ]
Qc 
3[ H 2 ][ C2 H 2 ]
2[ CH 4 ]
Qc 
[ C2 H 2 ]  [ H 2 ] 3
[CH 4 ]2
Qc 
[C2 H 2 ][ H 2 ]3
[CH 4 ]
a.
b.
c.
d.
e.
5.
At a particular temperature,
2 NO2 (g) ⇌ N2 (g) + 2 O2 (g)
Kc = 2.5 x 10-8
2 NO2 (g) ⇌ 2 NO (g) + O2 (g)
Kc = 5.0 x 10-5
Use the above information to calculate the Kc for the reaction below at that temperature.
2 NO (g) ⇌ N2 (g) + O2 (g)
Kc = ?
a.
b.
c.
d.
e.
6.
Kc = 0.10 for the reaction below at a particular temperature.
2 SO2 (g) + O2 (g) ⇌ 2 SO3 (g)
What is Kc for the following reaction at the same temperature?
SO3 (g) ⇌ SO2 (g) + 1/2 O2 (g)
a.
b.
c.
d.
e.
7.
5.0 x 10-4
2.0 x 103
impossible to determine
1.3 x 10-12
2.5 x 10-5
3.2
5.0
0.32
10
impossible to determine.
What is Kc for the following reaction, whose Kp = 3.9 x 10-2 at 1000 K?
CO (g) + Cl2 (g) ⇌ COCl2 (g)
a.
b.
c.
d.
e.
8.
At a particular temperature, the pXe in the following reaction is 1.7 x 10-2 atm at
equilibrium. What is Kp?
I2 (s) + 3 XeF2 (s) ⇌ 2 IF3 (s) + 3 Xe (g)
a.
b.
c.
d.
e.
9.
4.9 x 10-6
1.7 x 10-2
59
5.1 x 10-2
impossible to determine
The reaction A + 2 B ⇌ C + D has Kc = 8. At a particular moment in time, [A] = [B] =
0.2 M, [C] = 0.06 M, and [D] = 0.8 M. Which of the following statements is true?
a.
b.
c.
d.
e.
10.
3.2
3.9 x 10-2
26
4.8 x 10-4
impossible to determine.
Q < K and the reaction is proceeding to the right.
Q > K and the reaction is proceeding to the left.
Q < K and the reaction is proceeding to the left.
Q > K and the reaction is proceeding to the right.
The reaction is at equilibrium.
The reaction 2 NH3 (g) ⇌ N2 (g) + 3 H2 (g) has Kc = 9.0 at a particular temperature. At
equilibrium, [H2] = 0.32 M and [N2] = 0.10 M. What is [NH3] at equilibrium?
a.
b.
c.
d.
e.
2.0 x 10-2 M
3.6 x 10-4 M
2.8 x 10-3 M
2.6 x 10-3 M
cannot be determined without the temperature.
11.
2 NO (g) + O2 (g) ⇌ 2 NO2 (g)
1.000 atm of NO and 1.000 atm of O2 were placed in a container, and the reaction
allowed to reach equilibrium. At equilibrium, PO2 = 0.506 atm. What is Kp?
a.
b.
c.
d.
e.
12.
CO (g) + H2O (g) ⇌ CO2 (g) + H2 (g)
2.00 M CO and 1.00 M H2O were placed in a flask and allowed to reach equilibrium at a
particular temperature where Kc = 1.56. What is the [CO] at equilibrium?
a.
b.
c.
d.
e.
13.
impossible to determine
0.26 M
5.3 x 10-2 M
0.72 M
0.74 M
In the following reaction, which has Kc = 3.1 x 104 and Ho = -1376 kJ, 1.0 mol of each
substance is introduced into a 1.0 L vessel in the presence of a catalyst and allowed to
reach equilibrium and a constant temperature.
C2H4 (g) + 3 O2 (g) ⇌ 2 CO2 (g) + 2 H2O (l)
If argon (Ar) gas is now added to the vessel, what will happen?
a.
b.
c.
d.
e.
15.
1.27 M
0.27 M
0.73 M
1.73 M
none of the other answers
2 HI (g) ⇌ H2 (g) + I2 (g)
At a particular temperature, a vessel containing the above reaction was found to contain
[H2] = 0.26 M and [I2] = 0.28 M. What is [HI] at equilibrium?
a.
b.
c.
d.
e.
14.
1.3 x 104
3.2 x 102
2.1 x 105
1.6 x 102
impossible to determine
the equilibrium concentrations will stay the same.
[CO2] will decrease and [C2H4] will increase.
[CO2] will increase and [C2H4] will decrease.
all concentrations will increase.
all concentrations will decrease.
In the following reaction, which has Kc = 3.1 x 104 and Ho = -1376 kJ, 1.0 mol of each
substance is introduced into a 1.0 L vessel in the presence of a catalyst and allowed to
reach equilibrium and a constant temperature.
C2H4 (g) + 3 O2 (g) ⇌ 2 CO2 (g) + 2 H2O (l)
If the volume of the vessel is decreased, what will happen?
a.
b.
c.
d.
e.
the concentrations will all increase, but the reaction will then not shift.
[CO2] will decrease and [C2H4] will increase.
[CO2] will increase and [C2H4] will decrease.
the concentrations will stay the same, and the reaction will then not shift.
the concentrations will all decrease, but the reaction will then not shift.
16.
In the following reaction, which has Kc = 3.1 x 104 and Ho = -1376 kJ, 1.0 mol of each
substance is introduced into a 1.0 L vessel in the presence of a catalyst and allowed to
reach equilibrium and a constant temperature.
C2H4 (g) + 3 O2 (g) ⇌ 2 CO2 (g) + 2 H2O (l)
If the temperature is now raised, what will happen to the equilibrium concentrations?
a.
b.
c.
d.
e.
17.
In the following reaction, which has Kc = 3.1 x 104 and Ho = -1376 kJ, 1.0 mol of each
substance is introduced into a 1.0 L vessel in the presence of a catalyst and allowed to
reach equilibrium and a constant temperature.
C2H4 (g) + 3 O2 (g) ⇌ 2 CO2 (g) + 2 H2O (l)
If more CO2 is now added to the flask, what will happen?
a.
b.
c.
d.
e.
18.
HBr
HF
HNO2
HClO3
HCN
What is the pH of a 3.22 x 10-4 M solution of HCl, to the correct number of significant
figures?
a.
b.
c.
d.
e.
21.
Ca(OH)2
NH3
CH2COOH
H3O+ (aq)
F-
A 1.2 x 10-3 M solution of one of the following acids has a pH of 2.92. Identify the acid:
HF, HNO2, HBr, HClO3, HCN
a.
b.
c.
d.
e.
20.
the reaction shifts from right-to-left, and Kc stays unchanged.
the reaction shifts from left-to-right, and Kc stays unchanged.
the reaction shifts from right-to-left, and Kc decreases.
the reaction shifts from left-to-right, and Kc decreases.
the reaction shifts from left-to-right, and Kc increases..
Which of the following is an Arrhenius base?
a.
b.
c.
d.
e.
19.
[CO2] will decrease and [C2H4] will increase.
the concentrations will stay the same.
[CO2] will increase and [C2H4] will decrease.
all concentrations will increase.
all concentrations will decrease.
3.492
3.49
3.5
3
impossible to determine
Which of the statements is true about pure water, H2O (l).
a.
b.
c.
d.
e.
All three statements are true.
None of the three statements is true
[H3O+] = 1.0 x 10-7 M.
[H3O+][OH-] = 1.0 x 10-14
pH = 7.00
22.
Which of the following is not a Bronsted base? NH3, F-, H2O, CH3COOa.
b.
c.
d.
e.
23.
The pH of a solution is 4.24. What is its [OH-]?
a.
b.
c.
d.
e.
24.
HNO2 / NO3H2SO4 / HSO4F- / HF
HS- / S2HPO3- / H2PO3
Which of the statements is true about the equilibrium below?
HClO (aq) + IO- (aq) ⇌ ClO- (aq) + HIO (aq)
a.
b.
c.
d.
e.
26.
1.738 x 10-10 M
5.754 x 10-5 M
0.0000575 M
5.754 x 10-19 M
0.6274 M
Which of the following is not a conjugate acid/base pair?
a.
b.
c.
d.
e.
25.
they are all Bronsted bases.
H2O
FNH3
CH3COO-
IO- is the stronger base, and Kc > 1
ClO- is the stronger base, and Kc < 1
IO- is the weaker base, and Kc > 1.
HClO is the stronger acid, and Kc < 1.
HIO is the stronger acid, and Kc < 1.
Rank the following acids according to their acid strength, from strongest to weakest.
a.
b.
c.
d.
e.
HNO2 > HCOOH > HBrO > HCN
HCN > HBrO > HCOOH > HNO2
all are weak acids, and therefore have the same acid strength
HNO2 > HCOOH > HClO2 > HCN
HCN > HClO2 > HCOOH > HNO2
27.
The pH of a 1.0 M solution of NaOH is
a.
b.
c.
d.
e.
28.
What is the pOH for a 0.60 M solution of HNO2?
a.
b.
c.
d.
e.
29.
12.31
1.69
13.78
0.22
impossible to determine.
The pH of a solution of HBrO with pOH = 11.58 is
a.
b.
c.
d.
e.
30.
14.00
1.00
1.0 x 10-7
0.00
7.00
2.42
11.58
2.6 x 10-12
1.58
0.0038
[H3O+] = 3.4 x 10-2 M for a 0.70 M solution of a weak acid (HA). What is the percent
ionization?
a.
b.
c.
d.
e.
4.9%
3.4%
42%
1.1%
2.1%
Useful Information
Acid Ka values
---------------------------------------------HIO3
1.6 x 10-1
HClO2
1.12 x 10-2
HNO2
7.1 x 10-4
HF
6.8 x 10-4
HCOOH
1.8 x 10-4
C6H5COOH
6.3 x 10-5
CH3COOH
1.8 x 10-5
CH3CH2COOH
1.3 x 10-5
HClO
2.9 x 10-8
HBrO
2.3 x 10-9
HCN
6.2 x 10-10
HIO
2.3 x 10-11
R = 0.082 L.atm/mol.K
Kp = Kc (RT)Δn
VERSION 0
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