Analyses of reaction schemes using De Donder relations

The use of De Donder relations is addressed for analysis of reaction scheme s to describe the kinetics of overall reactions. These relations provide a simple means of determining the number of kinetic parameters required to ca lculate the overall reaction rate. These kinetic parameters for gaseous rea ctions are controlled by quasi-equilibria between the reactants and/or prod ucts of the overall reaction with the transition states of the elementary s teps, and they are not determined by the properties of the stable reaction intermediates. For surface reaction schemes, one additional kinetic paramet er is required for each stable surface species that becomes abundant on the surface. De Donder relations offer a rigorous approach for assessing wheth er a reaction scheme contains a rate determining step, and they provide a c onvenient means of deriving a series of rate expressions for cases where sp ecific steps are assumed to be rate determining. In addition, these relatio ns make it possible to calculate the maximum rate at which a given transiti on state may contribute to the overall reaction rate, providing a necessary condition for assessing the participation in the overall reaction scheme o f transition states identified by quantum-chemical calculations. (C) 1999 A cademic Press.