Thermodynamic parameters of reaction Me4+ + e ↔ Me3+ (Me Am, Ce) in organic and water-acetonitrile solutions of potassium tungstophosphates

Oxidizing potentials of reversible Me(4)-Me(3) pair, where Me = Am, Ce in aqueous and water-acetonitrile solutions of potassium tungstophosphate (TP) in a wide range of solution pH (0 - 7.7) and temperature (25 - 42 deg C), have been measured by potentiometric method. The shift of oxidizing potential to the negative region, as compared with its standard value, is shown to reach 1.25 V both for Am and Ce. The value of thermodynamic parameters (ΔG298, ΔH and ΔS) of the reaction in the title have been calculated. It has been ascertained that the contribution of energy component into the change of Gibbs free energy of the electrochemical reaction is much greater than the contribution of structural component. Parameters of a similar reaction for berkelium in TP solution have been evaluated. 9 refs., 2 figs., 2 tabs