Relation Between Rate Constants of Forward and Reverse Non-Equilibrium Reactions

5 Relation Between Rate Constants of Forward and Reverse Non-Equilibrium Reactions 

As stated above, under certain conditions, the kinetics of chemical reactions is defined by equations involving only total concentrations and macroscopic rate constants. In the state of thermodynamic equilibrium, the overall reaction rates are zero, and this permits to establish a relation between equilibrium concentrations and macroscopic rate constants. On the other hand the equilibrium concentrations are related via the thermodynamic equilibrium constants K which themselves do not depend on the reaction mechanism and are expressed through partition functions of reacting molecules (see Chapter I). This establishes the relation between equilibrium constants and the rate constants for forward and reverse reactions. Though this relation indisputable for equilibrium reactions, i.e. for reactions for which the perturbation of the Boltzmann distribution is small at any stage of the reaction, for non-equilibrium reactions the above relation is not strictly justifiable. 

As a simple example take the thermal dissociation of diatomic molecules (forward reaction) and atomic recombination (reverse reaction) in the heat bath 

Even if the reaction proceeds with strong perturbation of tbe Boltzmann distribution close to the dissociation limit, as commonly accepted, the non-equilibrium rate constants k igg 

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