Article révisé par les pairs
Résumé : 1. It is shown that for complex reactions of the type of the atomic halogenation reactions the real rate cannot be distinguished from the rate calculated by the usual steady state treatment if kp/kt < 2ϵ/0,693 (A)0; kp and kt are the rate constants of the chain propagation and termination and ϵ/(A)0 the relative accuracy of measuring initial concentrations (A)0. This means that the time required for a measurable amount of reaction is large compared to the lifetime of the chain. The ratio of the concentrations of two chain carriers is practically equal to the steady state ratio after a time which is large compared to the lifetime of one chain carrier. The conditions are discussed under which the concentration of the chain carriers must be low and the chains long. — 2. These considerations permit one to describe the conditions which are necessary for integrating the equations representing the rate of formation and disappearance of the intermediates and which are necessary for the calculation of the ratios of reaction rates in steady and intermittent light. — 3. It is shown that the photochlorinations of C2Cl4 and C2HCl5 previously studied satisfy the above conditions. Preliminary results with intermittent light yield values for the frequency factors of elementary reactions in agreement with previous estimates. Copyright © 1956 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim