Kinetic Irreversibility of Chemical Reactions

Sometimes partial thermodynamic equilibria between some reaction groups may happen at the stationary occurrence of compHcated stepwise processes. Unlike true (fuU) equihbria, the partial equihbria occur with the boundary conditions that contain the values of the chemical potentials of intermediates (i.e., the concentrations of intermediates) that are deter mined by the stationary states. 

An important consideration is the variations in thermodynamic rushes of the reaction groups in elementary reactions that are not in the partial 

Let us find the correct thermodynamic criteria of kinetic irreversibility of chemical reactions. It is evident for an elementary reaction ij that the statement 

the correct thermodynamic criterion of the kinetic irreversibility at any step in the chemical transformation chain is a considerable (against quantity RT) change in the chemical potential of the reaction groups related to this step—that is, A j RT. Note that the criterion is valid for both elementary and stepwise reaction, although in the latter case, one must consider the affinity for the stepwise transformation A,2 RT. 

An important consequence of the preceding consideration is the evident occurrence of the limitation (which is typicaUy not taken into account) for the maximum aUowed number of kineticaUy irreversible steps in the real stationary chemical reactions. Indeed, when the consecutive elementary chemical reactions proceed in the stationary mode, a total of affinity ArS of the stepwise reaction equals the sum of affinities of aU the elementary steps 

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