The Silver-Silver Oxide Electrode; the Entropy of Mercuric Oxide

Abstract

Stable, reversible Ag-Ag2O electrodes have been prepared by partial electrolytic reduction of Ag2O mixed with finely divided Ag in contact with a platinum wire. There is no apparent difference in the equilibrium electrode potential for annealed and unannealed Ag2O, provided that there is no great change in particle size. The average potential for the cell reaction(formula ommitted) is -0.2447 ± 0.001 v. at 25°. The free energy of formation of Ag2O at 25° is -2691 ± 10 cal./mole. Limited measurements of dE0/dT were made, and the value of -0.000201 ± 0.00001 v./deg. used to calculate ΔS0 = -9.27 ± 0.5 cal./deg. mole for the cell reaction. This value together with the entropies of Ag, Hg and Ag2O yields 17.4 ± 0.6 cal./deg. mole for the entropy of HgO at 298°K. Other cell data give concordant values for the entropy of HgO, but the result obtained from heat capacity data extrapolated from 15°K. is appreciably smaller. © 1962, American Chemical Society. All rights reserved.