PRACTICE EXAM III
CHEM 162
Dr. Overway
Instructions: Do not open this test booklet until you are instructed to do so. Show your work in order to
receive partial credit. Keep track of units and use the correct significant figures. The following
information may be useful during the exam.
Here are some things you may need.
E = E - (RT/nF) ln Q
-G = nFE
1 Amp = 1 C/sec
F = 96,485 C/mol e-
Grxn = (n*Gof prod) - (n*Gof react)
Horxn = (n*Hof prod) - (n*Hof react)
Sorxn = (n*Soprod) - (n*Soreact)
Go = Ho- TSo
GT = Ho- TSo
Species
ClO2-(aq)
ClO3-(aq)
O2 (g)
CO32- (aq)
Pb2+(aq)
PbCO3 (s)
Sof
(J/K mol)
101
162
205
-56.9
18.5
131.0
Thermodynamic data:
Species
Hof
(kJ/mol)
C2H4 (g)
52.47
CH4 (g)
-74.8
H2O (g)
-241.8
SO2 (g)
-296.8
H2O (l)
-285.8
H2 (g)
0.0
C3H6 (g)
20.4
NH3 (g)
-46.1
C3H3N (l)
172.9
O2 (g)
0.0
C2H4O (g)
-166
SO3 (g)
-396.0
2CO3 (aq)
-677.1
Pb2+(aq)
0.92
PbCO3 (s)
-699.1
Species
Gof
KCl(s)
Cl-(aq)
K+(aq)
CO32- (aq)
Pb2+(aq)
PbCO3 (s)
(kJ/mol)
-408.5
-131.2
-283.3
-527.8
-24.4
-625.5
CHEM 162-01
PRACTICE EXAM I
Name
.
1. Match the terms below with their definitions.
Terms
Definitions
___ Gibbs free energy
A) the enthalpy change when water rearranges itself around a solute
___ reaction coupling
B) the enthalpy change when a solute dissolves in a solvent
___ 2nd Law of Thermodynamics
C) the process by which a non-spontaneous reaction can become spontaneous
___ heat of solution
by the driving force of a more spontaneous reaction
___ exergonic
D) describes a process in which the free energy of the process decreases
___ heat of hydration
E) states that all spontaneous processes increase the entropy of the universe
F) used to describe the spontaneity of a reaction; the maximum available energy
to do work
2. (12 pts) What is the sign (+ or -) for S for the system for each of the following processes?
A) Wood burns producing carbon dioxide and water.
_____
B) Ice forms on the surface of a birdbath in winter.
_____
C) Water and acetone mix to form a liquid solution.
_____
D) A hot cup of coffee cools when left to stand.
_____
E) Solid iodine crystals form as a hot solution cools.
_____
F) A popsicle melts when left on a table.
_____
3. If a reaction has H<0 and S<0, under what conditions will it be spontaneous? Explain.
4. (6 pts) At what temperature will the following reaction become spontaneous (make sure you state
whether or not spontaneity occurs at a temperature above or below the temperature you determine see next to reaction)?
N2O4  2 NO2
Thermodynamic Values:
Hfo
Gfo
(kJ/mol) (kJ/mol)
N2O4 (g)
9.0
98
NO2 (g)
33
51
So
(J/K mol)
304
240
( Above or Below Temp =
)
5. (8 pts) Circle the one species of each pair that has the highest molar entropy.
a) NaCl (s) or MgCl2 (g)
b) HgO (s) or HgS (s)
c) Br2 (l) or I2 (s)
d) Cu (s) or Au (s)
6. (5 pts) How is it possible that some chemical reactions can have a Ssys <0 but still be spontaneous?
What else must be considered?
7.
8.
(16 pts) Draw a diagram of the battery (galvanic cell) that is composed of the following half-reactions. Label the
following parts: cathode, reaction at the cathode, anode, reaction at the anode, passive electrode, active electrode, salt
bridge, the overall reaction, calculate the ideal voltage (E)
a.
Mn3+(aq) + e -  Mn2+(aq)
Ereduction = +1.542 V
b.
Cu2+(aq) + 2 e -  Cu (s)
Ereduction = +0.3419 V
(8 pts) A digital watch battery draws 0.350 milliamperes of current, which is provided by a mercury battery whose net
reaction is:
HgO(s) + Zn(s)  ZnO(s) + Hg(l)
If a partially used battery contains 2.20 g of Zn and 6.00 g of HgO, how long will the watch
continue to run?
9.
(20 pts) Determine the oxidation number for each of the elements in the following compounds.
A) N2H4
N: ____ H: ____
B) N2O4
N: ____ O: ____
C) SF4
S: ____ F: ____
D) H2S
H: ____ S: ____
10. (12 pts) Balance the following redox equation and enter the coefficients for the reactants and products in order:
IO3- + Cr  I2 + Cr(OH)3 (basic)
11. Determine the Gibbs Free Energy (G) and Ksp for the following reaction at 88.7 C.
Pb2+ (aq) + CO32- (aq)  PbCO3 (s)