Reaction Rates and Concentration Effects

As an example, consider the reaction A + B — C, and let us assume that this is a nonelementary reaction. The rate equation in this case is Eq. (2.53), and we must find the values of a, p, and k. We do this by designing experiments in a way that isolates the contribution of each reactant to the initial rate, as shown in Table 2.1. 

Comparing the initial rates for runs 1 and 2, where [B]0 is doubled but [A]0 is unchanged, we see that the rate also doubles. Therefore this reaction is first order in B (P = 1). Similarly, comparing the initial rates for runs 2 and 3, where [A]0 is doubled but [B]0 is unchanged, shows that the doubling of [A]0 does not affect v0. This means that the reaction is zero order in [A] (a = 0). The overall rate equation is therefore Eq. (2.54). 

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