De Donder relations in mechanistic and kinetic analysis of heterogeneous catalytic reactions

The equations relating the rates of the elementary reactions to their affinities, known as the De Donder relations, are utilized within the theory of direct reaction routes (RRs). It is shown that any substitution of the surface coverages of the intermediates with the affinities of the elementary reactions is equivalent to a RR. Two types of direct RRs are defined. One of these produces "intermediate" reactions involving-the terminal species (reactants and products) and only one surface intermediate,while the other produces "overall" reactions involving only terminal species This formalism provides simple relations between the affinities of the elementary reactions and affinities of the reactions produced,by RRs. As a consequence, De Donder relations may-be naturally partitioned-into contributions coming from a finite and unique number of overall reactions produced by RRs. The results are applied to the particular case of rate-determining-step approximation in kinetics.