Intrinsic versus thermodynamic contributions to electrochemical reactivity

6 INTRINSIC VERSUS THERMODYNAMIC CONTRIBUTIONS TO ELECTROCHEMICAL REACTIVITY 

At several points in the foregoing description of electron-transfer models, it was found convenient to make a distinction between so-called intrinsic and thermodynamic contributions to the reaction barrier. Since such a distinction is central to both the theoretical treatment and data interpretation of electron-transfer processes [6, 65], it is worthwhile to clarify further the underlying notions that are involved. 

The intrinsic barrier therefore denotes the portion of the additional free energy possessed by the transition state with respect to the free energies of the adjacent ground (precursor and successor) states that arises only as a consequence of the non-equilibrium properties of the former. The elucidation of intrinsic barriers, at least relative values for a series of structurally related reactions or for different surface environments, is clearly of central fundamental importance in electrochemical kinetics. Although not often perceived in such terms, a major objective is therefore the utilization of strategies that correct, or otherwise allow for, the influence of thermodynamic contributions upon the experimental kinetic parameters. 

For solution reactants, the intrinsic barrier can be most directly related to the work-corrected standard rate constant for the single electron-transfer step 

provided Ap, AS t, and AH nt are themselves temperature-independent, AH nt can be obtained from the In kscorJ(llT) slope [eqn. (32)] and, since we anticipate that [40a] AS nt % 0 (Sect. 3.4), this yields AG, t since then AH t AG t. 

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