Ambiguity of the Definition

The true reaction path represented in Fig. 1.12 by a dashed line is a function of two variables f(X, 7). 

Such splits of the paths of the forward and the backward reaction were first found in the calculation of the PES of pericyclic reactions in the reaction coordinate regime. They were called the chemical hysteresis [61]. Of course, this hysteresis has no physical sense, although such a possibility was not originally rejected out of hand, it simply follows from the shortcoming of the procedure shown in Fig. 1.12. 

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Here, coordinate z is normal to the interface, and the integration is performed over the whole perturbed region. An important point in this formula is the lower integration limit, ZG. corresponding to the choice of the phase boundary , whose attribution is not self-evident. This ambiguity of the definition (66) is removed by the thermodynamics of charged interfaces based on the Gibbs electrocapillary equation (67) ... 

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