A complex reaction involving two series reactions can be of the type,

A reacts to give B, which is then transformed to C. Both the elementary reactions (1) and (2) exhibit first - order kinetics, that is,

For this reaction, [A] = [A]o exp (-k1t) …… (36)
It is difficult to derive the concentrations of [B] and [C] and will not be discussed. How the concentrations of the reactant (A), intermediate B and the product C vary with time are shown in below graph.

fig 6.15-Concentration versus time profiles of reactant A, intermediate B and product C in a series reaction of the type A

B

C