THERMODYNAMIC RELATIONSHIPS IMPORTANT FOR INTERPRETING APPARENT FORMAL POTENTIALS AND APPARENT REACTION ENTROPIES OF REDOX COUPLES IN PERMSELECTIVE MEDIA

Apparent formal potentials are measured for Os(bpy)(3)(3+/2+) exchange d in Nafion films on electrodes. The apparent formal potentials in the films are compared with the formal potential for Os(bpy)(3)(3+/2+) in solution using a description that assumes Os(bpy)(3)(2+) and Os(bpy)( 3)(3+) equilibrate with sodium ions in the bathing electrolyte solutio n. Good agreement is obtained between the experimentally determined va lues of the apparent formal potentials and the values expected using t he equilibrium model. Apparent reaction entropies are also measured fo r Os(bpy)(3)(3+/2+) exchanged in Nafion. Once the entropy of ion trans port is taken into account, it appears that the reaction entropy of Os (bpy)(3)(3+/2+) in Nafion is similar to that observed in aqueous solut ions. The environment in the vicinity of Os(bpy)(3)(3+) in Nafion appe ars to be very similar to the environment in the vicinity of Os(bpy)(3 )(2+) in Nafion. The results also demonstrate that there is a large en tropic contribution to the free energy of exchange, which is consisten t with the so-called hydrophobic effects observed by other workers.