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Chapter 12: Chemical Kinetics
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Self Quiz 2
Self Quiz 2
This activity contains 20 questions.
For the reaction
4NH
3
(
g
) + 5O
2
(
g
) ---> 4NO(
aq
) + 6H
2
O(
g
)
if Δ[H
2
O]/Δtime = 3.4 x 10
-2
M/s,
what is the value of -Δ[NH
3
]/Δtime?
1.4 x 10
-1
M/s
5.1 x 10
-2
M/s
-2.3 x 10
-2
M/s
2.3 x 10
-2
M/s
-3.4 x 10
-2
M/s
What is the average rate of appearance for product C over the time interval from 40.0 s to 120.0 s for the hypothetical reaction A + B ---> C? The data for the experiment is as follows:
time
conc. of C
0.00 s
0.00 M
40.0 s
0.33 M
80.0 s
0.58 M
120.0 s
0.70 M
6.4 x 10
-3
M/s
4.3 x 10
-3
M/s
7.2 x 10
-3
M/s
3.1 x 10
-3
M/s
4.6 x 10
-3
M/s
Which statement is generally true for reactions?
The rate of appearance of a product gradually increases as a reaction progresses.
The rate of appearance of a product is greater at the beginning of a reaction.
The rate of disappearance of a reactant gradually increases as a reaction progresses.
The rate of disappearance of a reactant is equal to the rate of disappearance of any other reactant in the reaction.
The rate of appearance of a product is equal to twice the rate of disappearance of a reactant if the product-reactant mole ratio is 1:2.
For the reaction A + B ---> C the rate doubles when the concentration of A doubles. When the concentrations of A and B are both doubled, the rate increases by a factor of 8. What is the rate law for this reaction?
rate = k[A][B]
rate = k[A][B]
2
rate = k[A][B]
3
rate = k[A]
2
[B]
2
rate = k[A]
2
[B]
What is the rate law for the hypothetical reaction X + 2Y ---> 2Z? The table below gives the initial concentrations and rates for several experiments.
Expt
[X]
[Y]
Initial rate, M/min
1
0.240 M
0.120 M
2.30 x 10
-4
2
0.720 M
0.240 M
2.07 x 10
-3
3
0.240 M
0.480 M
2.30 x 10
-4
4
1.440 M
0.240 M
8.28 x 10
-3
Rate = k[X][Y]
2
Rate = k[X]
2
[Y]
rate = k[X]
2
Rate = k[X]
4
Rate = k[X]
4
[Y]
The reaction A + B ---> 2C is second order with respect to A and -1 order with respect to B. If the reaction rate is 3.4 x 10
-2
M/min when [A] = 0.45 M and [B] = 1.28 M, what is the value of the rate constant?
1.3 x 10
-1
M
-2
·min
-1
2.1 x 10
-1
min
-1
2.1 x 10
-1
M
-1
·min
-1
5.9 x 10
-2
M
-1
·min
-1
9.7 x 10
-2
M·min
-1
The reaction X ---> products is first order, and the rate constant is 1.2 x 10
-4
min
-1
. If the original concentration of X is 1.35 M, how long (in hr) will it take the concentration of X to decrease by 85%?
1.6 x 10
4
hr
23 hr
48 hr
2.6 x 10
2
hr
1.4 x 10
3
hr
The reaction Z---> products is first order, and the rate constant is 8.7 x 10
-3
min
-1
. If the final concentration of Z was 0.045 M after 2.25 hr, what was the original concentration of Z?
0.014 M
0.088 M
0.075 M
0.046 M
0.15 M
The reaction C ---> products is first order, and the rate constant is 1.2 x 10
-2
min
-1
. How long (in hr) will it take for the concentration of C to fall to 6.25% of its original concentration?
4.8 hr
2.3 x 10
2
hr
0.90 hr
3.6 hr
3.8 hr
Which relationship is
not
true?
t
½
(k = 1.7 x 10
-3
min
-1
) > t
½
(k = 1.0 x 10
-1
s
-1
)
t
½
(k = 3.0 x 10
-2
s
-1
) > t
½
(k = 4.0 x 10
-2
s
-1
)
t
½
(k = 6.93 x 10
-3
min
-1
) = t
½
(k = 1.16 x 10
-4
s
-1
)
t
½
(k = 3.6 x 10
-4
min
-1
) < t
½
(k = 3.0 x 10
-4
min
-1
)
t
½
(k = 2.0 x 10
-2
min
-1
) > t
½
(k = 2.5 x 10
-4
s
-1
)
The reaction 2X ---> products is a second-order reaction, and the rate constant is 8.8 x 10
-3
1/M·s. If the initial concentration of X is 3.00 M, how many seconds does it take for the concentration of X to drop to 0.70 M?
200 s
124 s
492 s
261 s
9.6 x 10
-3
s
Which elementary step is
not
matched correctly with its molecularity classification?
(CH
3
)
2
CHI(
g
) ---> (CH
3
)
2
CH
+
(
g
) + I
-
(
g
) : unimolecular
2NO
2
(
g
) ---> NO
3
(
g
) + NO(
g
) : bimolecular
2NO(
g
) + O
2
(
g
) ---> 2NO
2
(
g
) : termolecular
Br(
g
) + Br(
g
) + N
2
(
g
) ---> Br
2
(
g
) + N
2
(
g
) : tetramolecular
H
2
O
2
(
aq
) + I
-
(
aq
) ---> OI
-
(
aq
) + H
2
O(
l
) : bimolecular
Which statement is true concerning this mechanism?
Step 1.
2NO
2
(
g
) ---> NO
3
(
g
) + NO(
g
)
Step 2.
NO
3
(
g
) + CO(
g
) ---> NO
2
(
g
) + CO
2
(
g
)
The first step in this mechanism is unimolecular.
The second step of the mechanism is bimolecular.
NO
2
is a reactive intermediate in this mechanism.
One of the products in the overall reaction is NO
3
.
According to the overall equation, 2 moles of NO
2
will produce 1 mole of CO
2
.
The elementary step that is
not
matched correctly with its rate law is
2NO(
g
) ---> N
2
O
2
(
g
) : rate = k[NO]
2
.
Ar(
g
) + I(
g
) + I(
g
) ---> Ar(
g
) + I
2
(
g
) : rate = k[Ar][I]
2
.
Cl
2
(
g
) ---> 2Cl(
g
) : rate = k[Cl
2
].
2F(
g
) + Ne(
g
) ---> F
2
(
g
) + Ne(
g
) : rate = k[F][Ne].
Br(
g
) + Cl(
g
) + N
2
(
g
) ---> BrCl(
g
) + N
2
(
g
) : rate = k[Br][Cl[N
2
].
The mechanism that is consistent with the rate law rate = k[D]
2
for the reaction D + E ---> F + G is
Step 1.
D + D ---> K, slow
Step 2.
K + E ---> F + G, fast.
Step 1.
C + D ---> F + G.
Step 1.
D + D ---> F + H, fast
Step 2.
H + E ---> G + D, slow.
Step 1.
D ---> F + J, slow
Step 2.
J + E ---> G, fast.
Step 1.
D + D ---> F + H, slow
Step 2.
H + E ---> G + D, fast.
Which is
not
characteristic of the relationship between activation energy and the distribution of collision energies?
As the temperature increases, the distribution shifts to higher energies.
At a given temperature the fraction of molecules having the activation energy will decrease for a sequence of reactions with larger and larger activation energies.
As the temperature increases, the fraction of collisions with higher energies increases.
The fraction of collisions having an energy greater than the activation energy is directly proportional to the temperature.
As the temperature decreases, the distribution shifts to lower energies.
Which statement concerning two reactions is
not
true, assuming they are carried out at the same temperature and have the same frequency factor A?
Reaction 1
E
a
= 40 kJ/mole
Energy of reaction = +20 kJ/mole
Reaction 2
E
a
= 30 kJ/mole
Energy of reaction = -20 kJ/mole
Reaction 2 is faster than Reaction 1.
The reverse reaction of Reaction 1 is slower than Reaction 2.
Reaction 2 is more exothermic than Reaction 1.
Reaction 1 is faster than the reverse reaction of Reaction 2.
The reverse reaction of Reaction 1 is faster than the reverse reaction of Reaction 2.
Find the temperature (in °C) at which the rate constant of a give reaction is k
2
= 2.4 x 10
-2
/M·s, if k
1
= 8.1 x 10
-10
/M·s at 25 °C and E
a
= 85 kJ/mole for the reaction.
-75 °C.
-274 °C.
6.0 x 10
2
°C.
-247 °C.
3.2 x 10
2
°C.
A catalyzed reaction has this two-step mechanism:
Step 1.
2X + Z ---> Y + W, slow
Step 2.
Y + T ---> Z + W, fast.
Which statement is correct?
Only Y is a catalyst.
Only Z is a reaction intermediate.
Both Y and Z are reaction intermediates.
Both X and Z are reactants.
Y is a reaction intermediate, while Z is a catalyst.
An example of homogeneous catalysis is
producing saturated fats from the reaction of unsaturated fats with H
2
in the presence of a nickel metal catalyst.
catalytic converters in automobiles.
the decomposition of O
3
(
g
) to O
2
(
g
) using Cl(
g
) atoms as a catalyst.
using MnO
2
(
s
) to decompose H
2
O
2
(
aq
).
producing NH
3
by the reaction N
2
(
g
) + 3H
2
(
g
) ---> 2NH
3
(
g
) in the presence of iron metal.
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