20 Questions from past exams.
Practice for speed. Aim
for 1 minute per problem.
Constants and
formulas: exp(x) = ex
1 year = 365 days;
1 hr = 60 min; 1 min = 60 s
freezing point of water = 0.00°C = 273.15K
Gas constant: R = 0.08206 L-atm/mol-K = 8.314 J/mol-K
Arrhenius equation:
k = A exp(-Ea/RT)
ln(k2/k1)
= (Ea/R)(1/T1 -
1/T2)
first-order decay:
[C]=[C]oexp(-kt);
t1/2 = ln(2)/k
1.
Use the data for the
reaction 2A + B
C + D
[A] (mol/L)
[B] (mol/L)
initial
rate (mol/L-s)
0.2
0.1
5
0.2
0.2
20
0.6
0.1
15
to find the empirical rate law.
A)
rate = k[A][B]
B)
rate = k[A]2[B]2
C)
rate = k[A][B]3/2
D)
rate = k[A][B]2
E)
rate = k[A]2[B]
2.
The
activation energy of a reaction can be lowered by
______.
A)
raising the temperature
B)
removing products
C)
adding a catalyst
D)
adding more reactants
E)
lowering the temperature
3.
Predict
the overall rate law for the gas reaction consistent
with the elementary mechanism
(1)
O3 O2
+ O
(slow)
(2)
O + NO
NO2
(fast)
A)
rate = k[O3][NO]
B)
rate = k[NO][O3][O2]-1
C)
rate = k[O][NO]
D)
rate = k[O3]
E)
rate = k[O3][NO][O]
4.
A
first-order chemical decomposition AB
A + B has a rate constant of 0.023 s-1 at
300K. If the initial concentration of AB is 2.0 M,
what is the concentration of AB after 80 s?
A)
0.13M
B)
0.54M
C)
0.0043M
D)
1.00M
E)
0.32M
5.
How many
elementary reaction steps are there in this reaction
pathway?
A)
2
B)
4
C)
1
D)
3
E)
5
6.
In
Question 5 the energy change for the overall reaction is
A)
exothermic
B)
endothermic
C)
zero
D)
impossible to tell
7.
Rates
of most chemical reactions ______.
A)
are independent of temperature
B)
decrease with decreasing temperature
C)
decrease with increasing temperature
8.
The
rate of the following reaction in water
S2O82- + 2I-
2SO42- + I2
is
found to double when the concentration of I-
is doubled, and increases by a factor of 4 when both the
concentration of I- and S2O82-
are doubled. The rate law for the reaction is
A)
rate
= k [S2O82-] [I-]2
B)
rate
= k [I-]2
C)
rate
= k [S2O82-] [I-]
D)
rate
= k [S2O82-]
E)
rate
= k [I-]
9.
The reaction
2NO(g) + 2H2(g)
N2(g) + 2H2O(g)
obeys a rate law that is
first order in H2 and second order in
NO. Find the correct statement:
A)
The
overall order of the rate expression is 4.
B)
The
rate of disappearance of H2 is equal to the
rate of disappearance of NO.
C)
The
rate of appearance of N2 is twice the rate of
disappearance of NO.
D)
The
overall order of the rate expression is 2.
10.
The rate of the reaction xX
+ yY + zZ
PRODUCTS has the following dependence on reactant
concentrations:
[X]
[Y]
[Z]
rate
1
1
1
k
2
2
2
16k
1
1
2
2k
2
1
2
4k
The rate law for the reaction is
A)
rate
= k[X]2[Y][Z]
D)
rate
= k[X][Y]3[Z]
B)
rate
= k[X][Y][Z]
E)
rate
= k[X][Y][Z]2
C)
rate
= k[Y]2[Z]
F)
rate
= k[X][Y]2[Z]
11.
The
half-life of the first order photodecomposition of the
carcinogen nitrosodimethylamine is 30 min. How many
minutes will it take for 99.9% of a sample to decompose?
A)
1784
B)
692
C)
299
D)
157
E)
93
12.
Predict
the rate of the gas reaction
2NO2
+ O3
N2O5 + O2
according to the proposed elementary mechanism:
(1)
NO2
+ O3
NO3 + O2
(slow)
(2)
NO3
+ NO2
N2O5
(fast)
A)
rate = k[NO2][O3]
D)
rate = k[NO2]2
B)
rate = k[NO2][O3]2
E)
rate = k[NO2]
C)
rate =k[NO2]2[O3]
13.
The
rate constant of an elementary reaction A+B C+D
is two-thirds the rate constant of the reverse reaction A+B
C+D at the same temperature. The correct statement is:
A)
The
activation energy of the forward reaction is greater
than the activation energy of the reverse reaction.
B)
The
activation energy is the same in both directions, so the
reverse reaction must be catalyzed while the forward
reaction remains uncatalyzed.
C)
The
activation energy of the reverse reaction is greater
than the activation energy of the forward reaction.
14.
The
rate law for the elementary reaction mechanism
(1)
2NO
N2O2
(rapid equilibrium)
(2)
N2O2 +
O2
2N O2
(slow)
is expected to be
A)
first-order
in NO and first-order in O2.
B)
second-order
in NO and second-order in O2.
C)
second-order
in NO and first-order in O2.
D)
first-order
in NO and second-order in O2.
E)
second-order
in NO and independent of O2.
F)
none
of the above.
15.
A certain
reaction for which the activation energy is 80 kJ/mole
proceeds very slowly at 300K. When the temperature
is increased to 400K the rate constant of the reaction
increases by a factor of
A)
2
x 108
D)
6
x 105
B)
1
x 104
E)
3
x 103
C)
5
x 102
16.
What are the
units of the rate constant k for a bimolecular
reaction?
A)
(mols/liter)2
s-1
D)
(mols/liter)-2
s-2
B)
(mols/liter)-1
s-2
E)
(mols/liter)-1
s-1
C)
(mols/liter)-2
s-1
17.
Which rate
law has an overall order of 1.5?
A)
rate = k[A][B][C]-1
D)
rate = k[A]2[B]1/2
B)
rate = k[A]2[B]1/2[C]-1
E)
rate = k[A][B][C]1/2
C)
rate = k[A][B]
18.
A
proposed mechanism for the decomposition of hydrogen
peroxide is
(1)
H2O2
+ I-
H2O + IO-
(slow)
(2)
IO-
+ H2O2
H2O + O2 + I-
(fast)
Find the statement that is false:
A)
The
overall reaction is 2H2O2
2H2O + O2.
B)
The
first step in the mechanism is the rate-determining
step.
C)
I- is a
catalyst.
D)
IO-
is an intermediate.
E)
The
rate expression is independent of the
concentration of I- .
19.
Predict
the rate of the reaction
Cl2
+ CO COCl2
according to the proposed elementary mechanism:
(1)
Cl2
2Cl
(rapid equilibrium)
(2)
Cl +
CO COCl
(rapid equilibrium)
(3)
COCl +
Cl2
COCl2 + Cl
(slow)
A)
rate = k[Cl2][CO]
D)
rate = k[Cl2]1/2[CO]
B)
rate = k[Cl2]3/2[CO]
E)
rate = k[Cl2][CO]2
C)
rate =k[Cl2]2[CO]
20.
The
carbon-14 nucleus decays by beta emission according to a
first-order rate law with a half-life of 5730 years. How much of an initial
sample of carbon-14 remains unreacted after 42,000
years?
C + D 
C+D at the same temperature. 
N2O2 
