Chapter 10
Chemical Kinetics
101
0
10
20
30
40
50
60
70
80
90
100
110
120
time/seconds
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.010
[NO ]
2
0.004 M
45 s
a
b
0.0015 M
50 s
1.
Distinguish between kinetic and thermodynamic regions of a reaction.
Concentrations change in the kinetic region, but they are constant at their equilibrium values in the
thermodynamic region.
3.
How does an increase in temperature affect the rate of reaction?
Increasing the temperature increases the rate of any reaction.
5.
Why do reaction rates slow as the reaction proceeds?
As the reaction proceeds, the reactant concentrations drop, which causes the reactions to slow.
7.
Distinguish between an average and instantaneous rates of reaction.
An average rate is a change in concentration divided by the time required to produce the change.
An
instantaneous rate is the rate at which the concentration is changing at any given instant.
9.
Consider the following plot of [NO
2
] versus time.
a)
What is the average rate of disappearance of NO
2
over the time
of the experiment?
∆
−
×
⋅
∆
5
1
2
[NO
]
(0.0100 M  0.0034 M)
=
= 5.5
10
M s
t
(0 s  120 s)
To determine the instantaneous rates, determine the slopes of the
tangent lines at the two times. The tangent lines are drawn in the
above figure
b)
Use the graphical methods presented in Section 10.1 to
determine the rate of disappearance of NO
2
at 20 seconds :
∆
−
×
⋅
∆
5
1
2
[NO
]
(0.0090 M  0.0050 M)
=
= 9
10
M s
t
(3 s  48 s)
at 80 seconds:
∆
−
×
⋅
∆
5
1
2
[NO
]
(0.0050 M  0.0035 M)
=
= 3
10
M s
t
(58 s  108 s)
11. What is the rate of formation (M
.
s
1
) of NOBr gas in a reaction in which 13.4 mmol of NOBr is produced in a 38.9
mL flask in 26.8 minutes?
∆
×
×
⋅
∆
×
6
7
1
[NOBr]
(13.4
10
mol)/0.0389 L
=
= 2.14
10
M s
60 s
t
26.8 min
min
13. What are the rates of appearance of NO
2
and O
2
when the rate of disappearance of N
2
O
5
is 2.0x10
5
M
.
s
1
?
2N
2
O
5
(g)
→
4NO
2
(g) + O
2
(g)
Define the rates of appearance of NO
2
and O
2
in terms of the rate of disappearance of N
2
O
5
by using the
coefficients from the equation.
[
]
[
]
[
]
∆
∆
∆
−
⇒
×
×
⋅
∆
∆
∆
2
2
5
2
5
5
1
NO
N O
NO
1
1
4
=
=
(2.0
10
) = 4.0
10
M s
4
t
2
t
t
2
[
]
[
]
[
]
∆
∆
∆
−
⇒
×
×
⋅
∆
∆
∆
2
2
5
2
5
5
1
O
N O
O
1
1
=
=
(2.0
10
) = 1.0
10
M s
t
2
t
t
2
15.
What is an exponential decay? What type of kinetics is characterized by an exponential decay?
A function, such as y = e
ax
, that decreases exponentially is an exponential decay. First order kinetics are
characterized by an exponential decay.
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Chemical Kinetics
102
17. A reaction has the experimentally determined rate law:
rate = k[A][B]
2
.
a)
What is the reaction order?
In a rate law, the sum of all the exponents in the rate law is called the
overall order
of the reaction.
overall order = 1+2 = 3
b)
What is the order with respect to A?
The exponent on each reactant exponent is referred to as the
reactant order
; in this case the order with respect to
reactant A is 1.
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 Spring '10
 Wilson
 Chemistry, Equilibrium, Kinetics, Rate equation

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