Reaction rate determined by multiple steps

For reactions in which the rate is determined not by a single elementary step but by multiple elementary steps, the overall affinity of the reaction is distributed among those multiple steps which determine the reaction rate as shown in Fig. 7-11 (b). The ratio of the forward to the backward reaction rate is then derived from Eqns. 7-40 and 7-43 to give Eqn. 7-60  

In the same way as Eqn. 7-45, the formal stoichiometric number, v, of the rate-detenniiiing steps can be expressed by Eqn. 7-51  

Ihis number v is the mean stoichiometric number of the rate-determining multiple steps. The mean stoichiometric number is thus represented by the energy average (afiiniiy average) of the stoichiometric niunbers v weighed with the step affinity 4gi in the respective rate-determining steps. 

The reaction affinity - AG and the ratio v /vj of the forward to the backward rate can be estimated, regardless of whether the reaction rate is determined by a single step or multiple steps. Thus, Eqn. 7-51 can be used to determine the mean stoichiometric number of the multiple rate-determining steps. 

In the reaction kinetics, the mean stoichiometric number is important to elucidate the reaction mechanism. 

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