Mechanistic classification. Multiple-step analyses

Before describing in detail the theoretical treatments appropriate to electrochemical reactions, it is desirable to outline the broad types of reaction mechanisms that are encountered. 

Several distinctly different classifications can be established. The simplest of these concerns the spatial position of the reaction site in the interfacial region. So-called outer-sphere reaction pathways are defined as those 

The distinction between the energetics of weak- and strong-overlap 

Outer-sphere pathways are normally expected to be of the weak-overlap type since reactant-electrode bond formation is, by definition, absent. Nevertheless, substantial energy differences between 0 and P, and R and S may occur (so-called double-layer effects, Sect. 3.5.2), at least as a result of electrostatic reactant-surface interactions. Inner-sphere pathways may be either of the weak- or strong-overlap type, depending on the strength and specificity of the reactant-surface binding (Sect. 3.5.1). 

The schematic free-energy profiles in Fig. 1 also illustrate the relationships between the various free-energy barriers of fundamental significance in electron-transfer kinetics. The activation free energy for the overall 

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