1
1. (6 pts) What is the oxidation state (number) for
a)
N
in
b)
I
c)
Cr in
in
NH 4Cl
IO3–
K 2Cr2O7
2. (8 pts) Indicate which of the following are oxidation-reduction reactions. Circle yes or no for each reaction.
a) PCl 3 + Cl2 —> PCl5
yes
no
b) Cu + 2 AgNO3 —> Cu(NO3) 2 + 2 Ag
yes
no
c)
yes
no
yes
no
CO2 + 2 LiOH —> Li2CO3 + H2O
d) FeCl 2 + 2 NaOH—> Fe(OH)2 + 2 NaCl
3.
(6 pts) Consider the following oxidation-reduction reaction.
2 Fe 3+ + 2 I–
2 Fe2+
—>
+ I2
Write the balanced oxidation and reduction half-reactions for this reaction.
Oxidation half-reaction :
Reduction half-reaction :
4.
(5 pts) How many moles of electrons are transferred in the following oxidation-reduction reaction?
CH4 + 2 O2
—>
CO2 + 2 H2O
5. (8 pts) Balance the following oxidation-reduction reaction in acidic solution, using the half-reaction
method.
Cr2O72–
+
I–
—>
Cr 3+
+
IO3–
2
6. Suppose the following data is obtained for the reaction CO + Cl2 —> COCl + Cl
[CO]o (mol/L)
1.00 x 102
2.00 x 102
3.00 x 102
1.00 x 102
2.00 x 102
Rate (mol L-1 s-1)
6.60 x 103
1.32 x 104
1.98 x 104
2.64 x 104
1.19 x 105
[Cl2] o (mol/L)
1.00 x 102
1.00 x 102
1.00 x 102
2.00 x 102
3.00 x 102
a) (6 pts) Write the rate law for this reaction.
b) (6 pts) Calculate the rate constant (be sure to include the units! ! ! )
7. Given the following reaction mechanism,
2 NO2Cl
ClO2 + N 2O + ClO
N2O + ClO2
NO 2 + NOCl
NOCl + ClO —> NO2 + Cl 2
Mechanisms will NOT be on this exam.
(fast equilibrium)
(fast equilibrium)
(slow)
a) (2 pts) What is the overall reaction?
b) (2 pts) List the intermediate(s) in the reaction.
c)
(6 pts) What is the order of reaction with respect to NO2?
3
8.
(9 pts) Nitryl chloride decomposes to nitrogen dioxide and chlorine, according to the following reaction.
2 NO2Cl —> 2 NO2 + Cl 2
The experimental rate law for this reaction is
Mechanisms will NOT be on this exam.
Rate = k [NO2Cl]
Which, if any, of the following mechanisms are consistent with the observed rate law? More than one answer is possible.
Cross out the mechanisms, if any, which are not consistent with the observed rate law.
a)
NO2Cl —> NO2 + Cl
Cl + NO2Cl —> NO2 + Cl 2
b) 2 NO2Cl
N 2O4 + Cl 2
N2O4 —> 2 NO2
c)
(slow)
(fast)
(fast equilibrium)
(slow)
2 NO2Cl
ClO2 + N 2O + ClO
N2O + ClO2
NO 2 + NOCl
NOCl + ClO —> NO2 + Cl 2
(fast equilibrium)
(fast equilibrium)
(slow)
9. (8 pts) The decomposition of nitrogen dioxide,
2 NO2
—> 2 NO + O 2
obeys the rate law:
Rate = k[NO 2]2
For this reaction the rate constant, k = 1.4 x 10–2 L mol -1 s -1 at 500 K. If the initial concentration is 1.00
mol/L, how long will it take for the [NO2] to decrease to 25.0 %?
10. (6 pts) Consider the reaction of nitrogen dioxide with oxygen,
NO2 + O 2 —> NO + O3
o
This reaction is endothermic with ∆H = +199 kJ//mol and the forward activation energy, Ea, is 209
kJ/mol. Draw a potential energy profile for this reaction. Your diagram should show the reactants,
products, transition state [X]‡, Ea and ∆Ho.
NOT be on this exam.
Energy
Reaction Coordinate
4
11. Answer the questions using the following half reactions:
E o (V)
Cl 2 + 2e– —> 2 Cl –
1.36
Cr2O72– + 14 H+ + 6 e– —> 2 Cr3+ + 7 H2O 1.33
O2 + 4 H+ + 4 e– —> 2 H 2O
1.23
ClO 2 + e – —> ClO 2–
0.95
+
–
Ag + e —> Ag (s)
0.80
Cu 2+ + 2e– —> Cu (s)
0.34
+
–
2 H + 2 e —> H 2
0.00
Co 2+ + 2 e– —> Co (s)
– 0.28
Cd2+ + 2 e– —> Cd (s)
– 0.40
Cr3+ + 3 e– —> Cr (s)
– 0.76
a) (2 pts) Which is the strongest reducing agent?
b) (2 pts) Is Cr 3+ capable of oxidizing Ag (s)?
c)
(2 pts) Is the reaction Cd (s) + 2 H+
—> H2 + Cd 2+
spontaneous?
e) (2 pts) Does Cu (s) dissolve in hydrochloric acid?
f)
(6 pts) Calculate ∆Go for the following reaction at 25 oC.
2 NaClO 2(aq) + Cl 2(g) —> 2 ClO2 (g) + 2 NaCl(aq)
g) (8 pts) An antique automobile bumper is to be chrome plated. The bumper is dipped into an acidic
Cr2O72– solution where it serves as the cathode of an electrolytic cell. If oxidation of H 2O occurs at the
anode, how many moles of oxygen gas will evolve for every 100 g of Cr (s) deposited? The atomic
mass of Cr is 52 g/mol.
.