The Rate-Limiting Step
A
B
C
Chemistry Essentials - 042
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The Rate-Limiting Step
B
C
E-ZPass
A
Chemistry Essentials - 042
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The Rate-Limiting Step
C
E-ZPass
B
Toll
A
Chemistry Essentials - 042
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Overall Reaction
Elementary Step
(fast)
+
Elementary Step
(slow)
Rate-Limiting Step
+
Elementary Step
(fast)
Reaction Mechanism
The Rate Law
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p
e
t
S
g
n
i
t
i
m
i
L
e
m
i
TStep 1:
Point A → Point B
Step
2:
Point
B
→
Point
C
+
E-ZPass
Toll
E-ZPass
Toll
Overall:
Point A → Point C
Toll
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p
e
t
S
g
n
i
t
i
m
i
L
e
m
i
TStep 1:
Point A → Point B
Step
2:
Point
B
→
Point
C
+
Overall:
Point A → Point C
Toll
Rate= [
Toll
E-ZPass
Toll
]
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p
e
t
S
g
n
i
t
i
m
i
Step
1:
NO
L
2
e
m
i
T
+
k1
+ NO2 → NO3 + NO
k2
(slow)
Step 2:
NO3 + CO → NO2 + CO2
(fast)
Step 3:
NO2 + CO → NO +CO2
(slow)
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k1
Step 1:
NO2 + NO2 → NO3 + NO
+
k2
(slow)
Step 2:
NO3 + CO → NO2 + CO2
(fast)
Step 3:
NO2 + CO → NO +CO2
(slow)
2
]
rate = k1[NO2
No
s
e
t
a
i
d
e
m
r
inte
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k1
Step 1:
NO + NO → N2O2
→
k-1
+
p
e
t
S
g
n
i
t
i
im
L
e
m
Ti Step
k2
2:
N2O2 + O2 → 2 NO2
(fast)
equilibrium
(slow)
Step 3:
2 NO + O2 → 2 NO2
=
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k1
Step 1:
NO + NO → N2O2
→
k-1
+
k2
Step 2:
N2O2 + O2 → 2 NO2
(fast)
equilibrium
(slow)
Step 3:
2 NO + O2 → 2 eNO
2
s
t
a
di
o
N
e
m
r
e
t
in
rate = k2[N2O2][O2]
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rate = k2[N2O2][O2]
2
k1[NO]
= k-1[N2O2]
k1
2
[N2O2] =
[NO]
k-1
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[N
rate = k2[N22OO2]2][O2]
= k1
k-1 [N
O] 2
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rate =
k1
2
[N
k2N
O
]
[O
]
O
]
2
2
2
k-1
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Did you learn?
The rate of the reaction is set by the
slowest elementary reaction.
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Acknowledgements
Jeremykemp. Blind Spot Diagram with Three Cars, (original upload date). Originally from en.wikipedia; description page is/was here. http://commons.wikimedia.org/wiki/File:Blindspot_three_cars_illus.svg.
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