Notional particles spatial distribution

In contrast to spatial distribution, the equilibrium energy distribution of adsorbed particles cannot be violated to any substantial degree by reaction since energy is rapidly transferred between adsorbed particles and solids. Therefore, the activated complex method may be applied to rates of surface reactions. For this we consider the activated complex (transition state) of a surface reaction as a likeness of adsorbed particle (21). But, assuming that each adsorbed particle occupies only one site, it is necessary, even in the simplest kinetic model, to consider that activated complexes are able to occupy not only one, but also several surface sites (21). For example, the usual picture of a reaction between two particles adsorbed on neighboring sites involves, in fact, the notion that the activated complex occupies both sites. When the activated complex occupies several sites, this does not create any difficulty for the theory since the surface concentration of activated complexes is an infinitesimal quantity, and so the possibility of overlapping the required sites is excluded. 

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