Kinetic parameters, inhomogeneity reactant

Thus for a case of nonuniform surfaces (eg, lateral interactions in the adsorbed layer), the equilibrium constant for the reaction route is expressed with a classical equation for the equilibrium constant, which is determined as the ratio of constants of the forward and reverse reactions. These constants do not include the lateral interactions in the adsorbed layer, hence analysis of the kinetic parameters in terms of their thermodynamic consistency can be also performed for reaction mechanisms with empty routes independent of the presence of lateral interactions. The same conclusion is vaHd for intrinsically inhomogeneous surfaces (so-called biographical nonuniformity), where the rate is obtained by summation of rates on active catalytic centers with different affinity to reactants and products. At the same time, the equihbrium constant is equal to unity in case of empty routes for each and every site. 

The concentrations of reactants are of little significance in the theoretical treatment of the kinetics of solid phase reactions, since this parameter does not usually vary in a manner which is readily related to changes in the quantity of undecomposed reactant remaining. The inhomogeneity inherent in solid state rate processes makes it necessary to consider always both numbers and local spatial distributions of the participants in a chemical change, rather than the total numbers present in the volume of reactant studied. This is in sharp contrast with methods used to analyse rate data for homogeneous reactions in the liquid or gas phases. 

An identical mathematical description of the kinetics of curing of reactants different in chemical nature and that obtained on the basis of fundamentally different experimental methods allows us to assume that this apparent selfacceleration course of some rheokinetic parameters is common to the processes of formation of materials with a crosslinked structure. It should be emphasized once more that the self-acceleration" effect must not be identified with the self-catalysis of the reaction of interaction between epoxy monomers and diamines which is studied in detail on model compounds [116, 117]. For each particular curing process the self-acceleration effect is influenced by the mechanism of network formatic, namely, chemical self catalysis [118], the appearance of local inhomogeneities [120], the manifestation of gel eff t [78], parallel course of catalytic and noncatalytic reactions [68]. It is probably true that the phenomena listed above may in one form or another show up in specific processes and make their contribution into self-acceleration of a curing reaction. 

It is important to note that while the rate of reaction depends on the concentrations of the reactants, the rate constant is independent of these and is the parameter commonly referred to in discussion of reaction kinetics. While for normal reaction systems the rate constant is naturally independent of time, for systems featuring an initially inhomogeneous distribution of reactants—as, for example, along the track of an a-particle or laser pulse immediately after discharge—the rate constant varies with time until homogeneity is achieved. 

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