Detailed balance in chemical kinetics as a consequence of microscopic reversibility

Abstract

The idea that the chemical principle of detailed balance is a consequence of microscopic reversibility is examined in terms of the stochastic theory of chemical reaction rates, particularly as developed by Snider. It is emphasized that detailed balance is a purely macroscopic requirement for all cases except those in which the chemical reaction mechanism contains a closed loop, or where forward and reverse rate constants for an elementary reaction step are measured in different experimental situations, each designed to isolate one unidirectional elementary reaction from its counterpart. Snider's theory is extended to a simpe triangular (closed‐loop) isomerization mechanism, and it is shown that detailed balance is not obtained as a result; this is in contrast to local‐equilibrium theories, for which the relationship between microscopic reversibility and detailed balance is well established. An attempt to overcome this difficulty by reformulating Snider's theory, in terms of the theory of lumping error, was only partly successful. The limitations of the present approach are discussed, and consequences for universally valid interpretations of phenomenological chemical kinetics are suggested.