Chemistry 118 - Principles of Chemistry
Spring, 2015
Problem Assignment 8 (due Wednesday, April 15, 2015)
1. Calculate ΔG° for each of the following reactions:
Fe2O3(s) + 3/2 C(s) → 2 Fe(s) + 3/2 CO2(g)
Fe2O3(s) + 3 C(s) → 2 Fe(s) + 3 CO(g)
Fe2O3(s) + 3 CO(g) → 2 Fe(s) + 3 CO2(g)
From your results, determine whether C or CO is the better reducing agent
for the conversion of Fe2O3 to Fe metal. Explain.
2. Write a balanced chemical equation for the reaction of liquid hydrazine and
gaseous dinitrogen tetroxide, which gives only nitrogen gas and water.
Calculate ΔH°, ΔS°, and the equilibrium constant for this reaction at 25 °C
and 200 °C.
3. Write a sequence of balanced chemical equations showing how sulfuric acid
may be obtained from hydrogen sulfide, H2S, as a starting material. (There
is a series of reactions that lead to H2SO4 from H2S.)
4. Calculate the equilibrium constant under standard conditions for the
production of hypochorite ion from the reaction of dichlorine oxide with
hydroxide.
Cl2O(g) + 2 OH- (aq) → 2 OCl- (aq) + H2O(l)
5.
Draw the Lewis structures and predict the molecular shapes for the following
fluorine containing compounds:
OF2, BrF3, ClF2+, AsF6-, BF4-
6. Hypobromite ion in aqueous solution disproportionates into bromide ion and
bromate ion. Calculate the equilibrium constant for this reaction under
standard conditions from the thermodynamic data tabulated below:
compound
(aq)
BrO- (aq)
BrO3- (aq)
Br-
7.
S° (J/mol K)
82
42
162
ΔHf° (kJ/mol)
-122
-94
-67
From the standard reduction potentials provided below, calculate the
reduction potential for the conversion of Cr2O72- to Cr2+ in an acidic solution.
Cr2O72-(aq) + 14 H+ + 6 e- → 2 Cr3+ + 7 H2O
Cr3+(aq) + e- → Cr2+
E°red = 1.33 volts
E°red = -0.407 volts
8.
The reduction of perxenate ion, XeO64-, to xenon is so favored
thermodynamically in acidic solution that it will oxidize Mn2+ to MnO4-, which
is one of the strongest common oxidizing agents found in a chemistry lab,
with the evolution of elemental oxygen. Write a balanced equation for this
redox reaction.
9.
Recently, the annual total consumption of carbonated beverages in the
United States reached 63 billion 12-ounce cans or bottles. If a 12-ounce can
has a volume of 355 mL and the concentration of dissolved CO2 is 0.15 M,
then calculate the total mass of CO2 used to make carbonated beverages
during that year.
10. Dioxygen difluoride, O2F2, is a potent fluorinating agent. It is made by the
irradiation of a mixture of O2 and F2 at -196 °C. Draw the Lewis structure for
this molecule and determine the bond order of each bond.
11. A commercial fluorine cell generates 3.3 kg of fluorine gas per hour by the
electrolysis of KF•2HF. Calculate the average current passing through this
cell.
12. When chlorine gas is bubbled through a basic solution containing iodide ions,
chloride ions and iodate ions are produced. If 0.216 L of chlorine gas at 0 °C
and 0.985 atm is needed to react completely with 50.0-mL of a iodide
solution, then determine the initial concentration of the iodide in that solution.
13. Under acidic conditions, sulfurous acid, H2SO3, disproportionates into SO42and S.
a. Write a balanced equation for this disproportionation reaction.
b. The reduction potential diagram is given below for [H+] = 1.0 M.
Calculate the cell potential for this disproportionation reaction.
SO4
2-
0.172 v
→
H2SO3
0.450 v
→
0.140 v
S
→
S2-
c. Calculate ΔG° and the equilibrium constant for this reaction at 25 °C.
14. Consider the lead-silver battery (Pb | Pb2+ (0.100 M) || Ag+ (0.250 M) | Ag).
E°red (Pb2+/Pb) = -0.126 volts, E°red (Ag+/Ag) = 0.800 volts
a. Calculate the cell potential when this battery is first connected at 25 °C.
b. Sodium sulfate was added to the compartment containing the lead half-cell
until [SO42-] = 0.100 M. If the measure cell potential is 1.096 volts,
determine the concentration of [Pb2+] ion remaining in solution and the
value of Ksp for PbSO4.
15. Ethanol, C2H5OH, is produced commercially by the fermentation of the
starch in grains. The molar heat of combustion of ethanol is -1368 kJ/mol.
a. Calculate the number of grams of ethanol that must be burned to raise the
temperature of one-liter of water from 20.0 to 90.0 °C.
b. If the molar heat of formation of CO2(g) and H2O(l) are -393.5 and -285.8
kJ/mol, respectively, then calculate the molar heat of formation of
C2H5OH.