Page 72 - Modeling of Chemical Kinetics and Reactor Design

42 Modeling of Chemical Kinetics and Reactor Design

Hence,

. 05
C * = K C (1-180)
H H 2
Substituting Equation 1-160 into Equation 1-168 gives

05 .
− ( r ) = k C C + k C K C
H 2 1 CH 4 H 2 2 C H 4 H 2
2
2
net (1-181)
.
= C C {k + k K 05 }
CH 4 H 2 1 2
2
Example 1-2
The overall reaction N + O → 2NO involves the elementary steps:
2
2

O + N  → NO + N *
*
k 1
2

N + O  → NO + O *
*
k 2
2
Write down equations for (–r ) and (–r ) .
O* net
N* net
Assuming these rates are equal to zero and C + C = C , a
O*
N*
T
) in terms of C , C ,
constant, derive an expression for (+r NO net T N 2
and C .
O 2
Solution
The net rates of disappearance of the free radicals (–r ) and
O* net
(–r ) are:
N* net
( −r O * ) net = k C C N 2 − k C N * C O 2 (1-182)
1
*
2
O
and
( −r N * ) net = k C N * C O 2 − k C C N 2 (1-183)
1
2
*
O
Assuming that (–r ) and (–r ) are zero, then
O* net N* net
kC C = k C C (1-184)
1 O * N 2 2 N * O 2