According to thermodynamic calculations, changes of the specific surface energy of a given electrode with intensive parameters, such as electrode potential, chemical potential of a component and temperature, should be the same in either phase of equilibrated partially miscible electrolytes. Analogously, in a given electrolyte, changes of the specific surface energy should be the same for electrodes composed of equilibrated phases. The thermodynamic theory was tested for gold in coexisting phases of water and isobutyl alcohol containing hydrochloric acid. Changes of the specific surface energy with electrode potential measured by Koesters laser interferometry, the potential dependence of impedance spectra, potentiodynamic polarisation curves and changes of the adsorbed mass obtained with the quartz frequency balance were the same in both phases.