D. A. Rockstraw, Ph.D., P.E.
NEW MEXICO STATE UNIVERSITY
Department of Chemical Engineering
Ch E 441 Chemical Kinetics and Reactor Engineering
Quiz 5 Open Book/Notes
The reaction oxidation of nitrous oxide 22 22 NOONO →
+
proceeds by the following mechanism:
23
23
32
2
2
2
1
NONONO
ONONO
NOONO
k
k
k
⎯→⎯+•
+⎯→⎯•
•⎯→⎯+
Additional information
[]
()
312
3
22EEE
NO
k
k
+>
>>
Determine the expected rate law rNO using pseudo-steady state hypothesis and
assuming that each step of the mechanism is an elementary reaction.
Indicate whether reaction rate increases or decrease with temperature. Why?
SOLUTION
Assume mechanism steps are elementary;
[][]
[]
[][]
NONOkr
NOkr
ONOkr
•=
•=
=
333
322
211
The net rate for NO3* is the sum of the individual reaction rates for NO3*
[][] [ ] [][]
NONO
kr
rNOkrrONOkrr NONONO •==−•==−== ••• 3
33
332222111 22
; ; 333
•••• ++= 3333 321 NONONONO rrrr
[][] [ ] [][]
NONO
k
NOkONOkrNO •−•−=
•3
3
3221 2
3
PSSH assumes net rate of NO3* is zero 0
3
=
•NO
r →
[]
[
][ ]
[]
NO
k
k
ONOk
NO
2
3
2
21
3+
=•
[][] [][]
[]
[] [][]
[]
NO
k
ONOk
kNO
NO
k
k
ONOk
kNONOkrNO ⎥
⎦
⎤
⎢
⎣
⎡
=
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
+
=•=
2
21
3
3
2
21
333
2
2
[][]
(
)
[][]
2
2
312
2
31
2
2
2
31 exp
2ONO
RT
EEE
A
AA
ONO
k
kk
rNO ⎟
⎠
⎞
⎜
⎝
⎛+−
==
rate decreases as temperature increases because of sign of exponential term