Abstract:
The absolute value of the standard potential of the hydrogen electrode is calculated on the basis of a value of –263.1 kcal mol–1 for [graphic ommitted], the standard chemical free energy of hydration of the proton. This quantity, in turn, is evaluated from the experimental value of [graphic ommitted], the standard real free energy of hydration, as measured by Randles, and the value of 0.13 V for χH2O, the surface potential of water at the air/solution interface. The reliability of the derivation of χH2O is much increased by using, as a basis, a value for g(Hg)H2O(dipole), the surface potential of water at the mercury/solution interface, derived from indirect experimental measurements. The values of g(M)H2O(dipole) on a number of other metals are correlated to the enthalpy of formation of oxides MO and the resulting linear relationship interpreted in terms of different interaction of water with different metal surfaces. The significance of εabs°(H+/H2), the absolute potential of the standard hydrogen electrode, and its relation to ΔMSϕ, the actual potential difference across the electrode/solution boundary (operative electrode potential) are discussed. An attempt to calculate ΔMSϕ for alkali metals is made on the basis of chemical potentials of electrons as calculated from the theory of metals. Incorrect conclusions in previous works on the significance of µMe, the chemical potential of electrons, are shown and discussed. Implications are extended to the field of potentials of zero charge.
