THE SQUARE SCHEME WITH THE ELECTROCHEMICAL REACTIONS AT EQUILIBRIUM - A STUDY BY DIFFUSION OR THIN-LAYER CYCLIC VOLTAMMETRY AND BY SCANNING POTENTIAL COULOMETRY

The four-member square scheme with the electrochemical reactions at equilibrium is analyzed for semi-infinite or thin layer cyclic voltammetry and for scanning potential coulometry. First order or pseudo-first order chemical reactions are considered. At slow sweep rates a monoelectronic reversible system is observed, situated at a potential E//K degree which is a function of the two equilibrium constants of the chemical reactions. These equilibrium constants can be calculated from the difference E//1 degree -E//K degree or E//2 degree -E//K degree ; E//1 degree and E//2 degree , the redox potentials of the electrochemical reactions, can be obtained for large sweep rates. The rate constant can be deduced from the theory of the EC mechanism when the chemical reaction is irreversible, applied to each half of the square scheme.