Temperature dependence of electrode reaction rates

The rate of an electrode process directly depends on magnitude, of the potential drop at the electrode-solution interface. Therefore, while determining the activation energy from the temperature dependence of the reaction rate, we would have to maintain constant not only such common independent variables as pressure P and concentration m, but also  

It is assumed here that the composition of the bulk phase is such that its constancy ensures also that of the surface concentration, i.e., there is no difference in the true and apparent activation energies. A corresponding correction factor has been described in Sections 2.1 and 4, and is not considered here. 

However, the magnitude of a single potential drop cannot be measured directly, therefore, it is not possible to control its constancy, i.e., we cannot conduct an experiment to determine the value similar to the energy of activation of a common chemical reaction. This value, which is impossible to measure is called, according to Temkin, the ideal activation energy. 

A practical activation energy can be experimentally found at a constant measured electrode potential, but usually this value has no definite physical meaning since the selection of the reference electrode is arbitrary. It acquires a definite physical meaning only when a reversible electrode is chosen as the reference one, on which equilibrium of the reaction of interest is achieved. In this case, the electrode potential being measured is the overpotential 

The activation energy found experimentally at a constant overpotential has been termed by Temkin the real activation energy 

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