Conditions for First‐ or Second‐Order Kinetics during Multiple Zone Reactions

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Abstract
The influence on observed reaction rates of isolating the reactants among a number of physically separated zones is considered from the standpoint first of the transition from second‐ to first‐order kinetics as the concentration of reacting species per zone becomes very small (of the order of 10 or less), and second from the standpoint of an initial nonuniform distribution of the reactants in the zones. The case of the numbers of reacting species being limited to even numbers only, as in free radical production and decay, is also treated explicity for a small number of zones. When the number of zones is large and the restriction to even numbers omitted, the over‐all observed reaction rate is exactly second order irrespective of the number of reacting species per zone, providing that the concentration distribution follows a multinomial (random) distribution.