CHEM 1412 Practice Exam 3 (Chapters 18, & 19)
1. Calculate S at 25C for the reduction of PbO(s), 2PbO(s) + C(s)  2Pb(s) + CO2(g) given these
absolute entropies:
A.
B.
C.
D.
E.
+198.8 J/K·mol
+488.0 J/K·mol
+353.6 J/K·mol
-203.3 J/K·mol
+203.3 J/K·mol
2. At 1500C the equilibrium constant for the reaction CO(g) + 2H2(g)
= 1.4  10-7. Calculate G for this reaction at 1500C.
A. 105 kJ/mol
B. 1.07 kJ/mol
C. -233 kJ/mol
D. -105 kJ/mol
E. 233 kJ/mol
CH3OH(g) has the value Kp
3. HI has a normal boiling point of -35.4C, and its Hvap is 21.16 kJ/mol. Calculate the molar entropy of
vaporization (Svap).
A. 598 J/K·mol
B. 68.6 J/K·mol
C. 75.2 J/K·mol
D. 0.068 J/K·mol
E. 89.0 J/K·mol
4. Ozone (O3) in the atmosphere can react with nitric oxide (NO):
O3(g) + NO(g)  NO2(g) + O2(g).
Calculate the G for this reaction at 25C. (H = -199 kJ/mol, S = -4.1 J/K·mol)
A.
B.
C.
D.
E.
1020 kJ/mol
-1.22  103 kJ/mol
2.00  103 kJ/mol
-1.42  103 kJ/mol
-198 kJ/mol
5. Calculate Kp at 298 K for the reaction SO2(g) + NO2(g)  SO3(g) + NO(g).
A.
B.
C.
D.
E.
6.99  10-7
5.71  10-8
14.2
475
1.42  106
6. Nitrosyl chloride (NOCl) decomposes at elevated temperatures according to the equation 2NOCl(g)
2NO(g) + Cl2(g). Calculate Kp for this reaction at 227C.
(For this reaction H = 81.2 kJ/mol, S = 128 J/K·mol)
A. 1.59  10-2
B. 2.10  10-7
C. 62.8
D. 4.90  106
E. 3.20  109
7. Determine S for the reaction SO3(g) + H2O(l)  H2SO4(l).
A.
B.
C.
D.
E.
169.2 J/K·mol
1343.2 J/K·mol
-169.2 J/K·mol
-29.4 J/K·mol
29.4 J/K·mol
8. For the reaction SbCl5(g)
SbCl3(g) + Cl2(g),
(SbCl5) = -334.34 kJ/mol
(SbCl3) = -301.25 kJ/mol
(SbCl5) = -394.34 kJ/mol
(SbCl3) = -313.80 kJ/mol
Will this reaction proceed spontaneously at 298 K and 1 atm pressure?
9.
What is the coefficient of water when the following equation is balanced in acidic aqueous solution?
–
Cr2O7 2– + Br  Cr 3+ + Br2
a) 5
10.
b) 6
c) 7
d) 8
Consider an electrochemical cell constructed from the following half cells, linked by a KCl salt
bridge.
 an Al(s) electrode in 0.5 M Al2(SO4)3 solution
 a Pb(s) electrode in 1.0 M Pb(NO3)2 solution
Which electrode is the anode?
11.
A.
Al
B.
Pb
C.
neither
For the reaction, 2Cr2+ + Cl2(g)  2Cr3+ + 2Cl-, Ecell is 1.78 V. Calculate Ecell for the related
reaction Cr3+ + Cl-  Cr2+ + (1/2)Cl2(g).
A.
1.78 V
B.
0.89 V
C.
-1.78 V
D.
-0.89 V
E.
none of these
12.
The overall reaction 2Co3+(aq) + 2Cl-(aq)  2Co2+(aq) + Cl2(g) has the standard cell voltage
Ecell= 0.46 V. Given that Cl2(g) + 2e-  2Cl-(aq), E = 1.36 V,
calculate the standard reduction potential for the following the half reaction at 25C:
Co3+ + e-  Co2+
A. 1.82 V
B. -0.90 V
13.
C.
0.90 V
D.
-1.82 V
E.
-1.36 V
Consider the following standard reduction potentials in acid solution:
Which is the weakest oxidizing agent in this list?
14.
15.
A.
Al3+(aq)
B.
Al(s)
C.
I-(aq)
D.
I2(s)
E.
Sn4+(aq)
How many faradays are transferred in an electrolytic cell when a current of 2.0 amperes flows for
12 hours?
A.
24 F
B.
8.6  104 F
C.
0.90 F
D.
6.2  10 -3 F
E.
1.1 F
How many coulombs of charge are required to cause reduction of 0.20 mole of Cr3+ to Cr?
A.
0.60 C
B.
3.0 C
C.
2.9  104 C
D.
5.8  104 C
E.
16.
9.65  104 C
According to the following cell diagram, which chemical species undergoes reduction?
Sn | Sn2+ || NO3- (acid soln), NO(g) | Pt
17.
18.
A.
Sn
B.
Sn2+
C.
NO3-
D.
NO
E.
Pt
For the reaction, 2Cr2+ + Cl2(g)  2Cr3+ + 2Cl-, Ecell is 1.78 V. Calculate Ecell for the related
reaction Cr3+ + Cl-  Cr2+ + (1/2)Cl2(g).
A.
1.78 V
B.
0.89 V
C.
-1.78 V
D.
-0.89 V
E.
none of these
Calculate Ecell for the following reaction:
2Fe2+(aq) + Cd2+(aq)  2Fe3+(aq) + Cd(s)
Fe2+(aq)  Fe3+(aq) 0.77V
A.
-0.37 V
B.
0.37 V
C.
-1.17 V
D.
1.17 V
E.
none of these
Cd2+(aq)  Cd (aq)
-0.4V
19.
20.
In the following half equation, which is the oxidizing agent?
NO3-(aq) + 4H+(aq) + 3e-  NO(g) + 2H2O
A.
NO3-
B.
H+
C.
e-
D.
NO
E.
H2O
For the reaction Ni2+(aq) + 2Fe2+(aq)  Ni(s) + 2Fe3+(aq), the standard cell potential Ecell is
A.
+2.81 V.
B.
+1.02 V.
C.
+0.52 V.
D.
-1.02 V.
E.
-2.81 V.
PART II SHOW YOUR WORK
1.
The reaction N2 (g) + 3H2 (g)
2NH3 (g) has ∆G° = –33.32 kJ/mol at 25°C.
What is ∆G at 25°C if the initial pressures of N2, H2, and NH3 are 2.0 atm each?
2. Calculate G° for the following reaction:
2 SO2 (g) + O2 (g)  2 SO3 (g)
H° = –196 kJ and S° = –191 J/K
3. Hydrogen peroxide (H2O2) decomposes according to the equation
H2O2(l)  H2O(l) + (1/2)O2(g).
Calculate Kp for this reaction at 25C. (H = -98.2 kJ/mol, S = 70.1 J/K·mol)
4.
i.How many grams of copper metal can be obtained by passing a current of 1.50 amp
through a solution of Cu2+ (aq) for 45 minutes?(Show calculation)
5. Given the following standard reduction potentials:
Pb2+ (aq) + 2e-  Pb(s)
E° = –0.126 V
Cu2+ (aq) + 2e-  Cu(s)
E° = +0.337 V
calculate E°cell for a voltaic cell based on these half-reactions.
6. Eocell for the following reaction is +0.13 V. What is the value of G° (in kJ) for the
reaction?
Pb (s) + 2 H+ (aq)  H2 (g) + Pb2+ (aq)
7. The reaction O2 (g) + 4 H+ (aq) + 4 Fe2+ (aq)  4 Fe3+ (aq) + 2 H2O (l) has
E° = +0.46 V. What is the value of the equilibrium constant for this reaction?