Chemistry 213
Exam IV - A
Spring 2010
Show all work and mark answers on the exam form. Clearly lable exam version on scantron
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) For the reaction
C2H6 (g)
1)
C2 H4 (g) + H2 (g)
H° is +137 kJ/mol and S° is +120 J/K · mol. This reaction is __________.
A) spontaneous only at high temperature
B) spontaneous only at low temperature
C) nonspontaneous at all temperatures
D) spontaneous at all temperatures
2) What is the oxidation number of bromine in the BrO3- ion?
A) -1
B) +7
C) +1
2)
D) +3
E) +5
3) Which element is reduced in the reaction below?
I- + MnO4- + H+
A) O
3)
I2 + MnO2 + H2 O
B) H
C) I
D) Mn
4) Which one of the following is always positive when a spontaneous process occurs?
A) Suniverse
B) Ssystem
C) Huniverse
D) Hsurroundings
E) Ssurroundings
1
4)
5) The standard emf for the cell using the overall cell reaction below is +2.20 V:
2Al (s) + 3I2 (s)
5)
2Al3+ (aq) + 6I- (aq)
The emf generated by the cell when [Al3+ ] = 4.5 × 10-3 M and [I-] = 0.15 M is ________ V.
A) 2.23
B) 2.30
C) 2.10
D) 2.20
E) 2.39
6) The electrode at which oxidation occurs is called the __________.
A) voltaic cell
B) reducing agent
C) oxidizing agent
D) cathode
E) anode
Table 20.2
Half-reaction
Cr3+ (aq) + 3eFe2+ (aq) + 2eFe3+ (aq) + eSn4+ (aq) + 2e-
6)
E° (V)
Cr (s)
-0.74
Fe (s)
Fe2+ (s)
-0.440
Sn2+ (aq)
+0.771
+0.154
7) The standard cell potential (E°cell) for the voltaic cell based on the reaction below is __________ V.
3Sn4+ (aq) + 2Cr (s)
A) -1.02
B) +2.53
2Cr3+ (aq) + 3Sn2+ (aq)
C) +1.94
2
D) -0.59
E) +0.89
7)
8) Given the thermodynamic data in the table below, calculate the equilibrium constant (at 298 K) for
the reaction:
2 SO2 (g) + O2 (g)
Substance
SO2 (g)
O2 (g)
SO3 (g)
8)
2 SO3 (g)
Hf° (kJ/mol) S° (J/mol · K)
-297
249
0
205
-395
256
A) 1.95
B) 1.06
C) 2.40 × 1024
D) 3.82 × 1023
E) More data are needed.
9) The standard cell potential (E°) of a voltaic cell constructed using the cell reaction below is 0.76 V:
Zn (s) + 2H+ (aq)
Zn2+ (aq) + H2 (g)
With PH2 = 1.0 atm and [Zn2+] = 1.0 M, the cell potential is 0.66 V. The concentration of H+ in the
cathode compartment is __________ M.
A) 1.0 × 10-12
B) 4.9 × 101
C) 2.0 × 10-2
D) 4.2 × 10-4
E) 1.4 × 10-1
3
9)
10) The thermodynamic quantity that expresses the degree of disorder in a system is __________.
A) enthalpy
B) bond energy
C) entropy
D) internal energy
E) heat flow
10)
11) The gain of electrons by an element is called __________.
A) reduction
B) fractionation
C) sublimation
D) disproportionation
E) oxidation
11)
4
Use the table below to answer the following three questions that follow.
Thermodynamic Quantities for Selected Substances at 298.15 K (25°C)
Substance
H°f (kJ/mol)
Calcium
Ca (s)
CaCl2 (s)
0
-795.8
0
-748.1
41.4
104.6
Ca2+ (aq)
226.7
209.2
200.8
0
222.96
Chlorine
Cl2 (g)
Cl- (aq)
Oxygen
O2 (g)
G°f (kJ/mol)
0
-167.2
S (J/K-mol)
56.5
-131.2
0
0
H2O (l)
-285.83
-237.13
Phosphorus
P2 (g)
144.3
103.7
218.1
-288.1
-269.6
311.7
-542.2
-502.5
325
0
-269.9
0
-300.4
31.88
248.5
-395.2
-370.4
256.2
PCl3 (g)
POCl3 (g)
Sulfur
S (s, rhombic)
SO2(g)
SO3(g)
205.0
69.91
12) The value of H° for the oxidation of solid elemental sulfur to gaseous sulfur dioxide,
S (s, rhombic) + O2 (g)
SO2 (g)
is __________ kJ/mol.
A) +11.6
B) +269.9
C) -269.9
5
D) -11.6
E) +0.00
12)
13) The value of S° for the oxidation of solid elemental sulfur to gaseous sulfur dioxide,
S (s, rhombic) + O2 (g)
13)
SO2(g)
is __________ J/K· mol.
A) -248.5
B) +248.5
C) -11.6
D) +485.4
E) +11.6
14) The value of G° at 373 K for the oxidation of solid elemental sulfur to gaseous sulfur dioxide,
S (s, rhombic) + O2 (g)
14)
SO2 (g)
is __________ kJ/mol. At 298 K, H° for this reaction is -269.9 kJ/mol, and S° is +11.6 J/K.
A) -274.2
B) -300.4
C) -4,597
D) +4,597
E) +300.4
15) What is the oxidation number of manganese in MnO2 ?
A) +3
B) +2
C) +4
15)
D) +7
16) Which reaction produces a decrease in the entropy of the system?
2H2 O (l)
A) 2H2 (g) + O2 (g)
CO2 (g)
B) CO2 (s)
CaO (s) + CO2 (g)
C) CaCO3 (s)
2CO (g)
D) 2C (s) + O2 (g)
E) H2 O (l)
H2O (g)
6
E) +1
16)
17) The standard cell potential (E°cell) for the reaction below is +1.10 V. The cell potential for this
reaction is __________ V when the concentration of [Cu2+] = 1.0 × 10-5 M and [Zn2+ ] = 1.0 M.
Zn (s) + Cu2+ (aq)
A) 0.80
Cu (s) + Zn2+ (aq)
B) 1.25
C) 1.40
D) 1.10
18) Consider the reaction:
Fe2 O3 (s)
Given the following table of thermodynamic data,
FeO (s)
Fe (s)
O2 (g)
Fe2 O3 (s)
E) 0.95
18)
FeO (s) + Fe (s) + O2 (g)
Substance
17)
Hf° (kJ/mol) S° (J/mol · K)
-271.9
0
0
60.75
27.15
205.0
-822.16
89.96
determine the temperature (in °C) above which the reaction is nonspontaneous.
A) 756.3
B) 618.1
C) This reaction is spontaneous at all temperatures.
D) 1235
E) 2438
7
19) A reaction that is spontaneous as written __________.
A) will proceed without outside intervention
B) is very rapid
C) is very slow
D) is also spontaneous in the reverse direction
E) has an equilibrium position that lies far to the left
8
19)