ENTROPY DIFFERENCES FOR SOME RELATED PAIRS OF COMPLEX IONS

Abstract

The temperature coefficient of e.m.f. of a cell consisting of a saturated calomel electrode and a redox electrode of K₄Fe(CN)₆ and K₃Fe(CN)₆ has been determined by e.m.f. measurements at a series of equimolal concentrations of the above salts and at temperatures of 20, 25, 30, 35 °C. The results for this calomel–redox cell are expressed by the equation E_CR⁰ = 0.1200 − 0.00214(t − 25), or for the redox electrode against a hydrogen gas electrode, E_HR⁰ = 0.3644 − 0.00280(t − 25), with E in V and t in °C. Analogous results are available in the literature for other such pairs of complex ions; an examination of these data leads to the hypothesis that the following trichelated pairs: Fe dip₃^2+/3+, Fe phen₃^2+/3+, Ru dip₃^2+/3+, are respectively nearly isentropic.