Educational problems in electrochemical thermodynamics

This article reviews educational problems of electrochemical thermodynamics required as introduction to any electrochemistry-related course. Specifically, the most important, electromotive force (EMF) equation, - is generally derived from Guggenheim's formulation of electrochemical potential. For this aim the more general equation for equilibrium between phases is introduced. Special attention is given to the measurement of electrode potential. Potential drop across metal|metal contacts, usually displayed in potential profiles of electrochemical cells, can be excluded from them. The conclusion is based on Lord Kelvin's formulation of the case, when metals are in contact, as "metallic zero". Concerning absolute potentials, for the cases when the electrode material does not participate in electrochemical reaction, it can be calculated from the Gibbs free energy of the corresponding chemical reaction occurring in solution. Accordingly, the absolute hydrogen electrode potential is determined by thermodynamics of H+/H2 reaction.