How is the rate law for for A+B = X -> C written?

Considering the following reaction:

A + B

k* k-*

X

k**

C

Do I have to describe the consumption speed of X by:

1. d(X)/dT= k^*(A)(B) - k^-*(X) - k^**(C)
2. d(X)/dT= k^*(A)(B) - k^-*(X)

or are both correct?
Serge Gomes (100572.3605@compuserve.com)

X is produced by the process you've labelled with '*' and destroyed by the processes labelled '-*' and '**'. If these are one-step processes, the net rate of change for X should be

d(X) dt

= k*(A)(B) - k-*(X) - k**(X)

so unless k^** is very small, the answer is 'none of the above'.

Author: Fred Senese senese@antoine.frostburg.edu

Copyright © 1997-2005 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 07/31/07.URL: http://antoine.frostburg.edu/chem/senese/101/kinetics/faq/stepwise-ratelaw.shtml