Absolute half-cell entropy

The absolute half-cell entropy is defined here as the entropy of the cell process $M\to M^{+}\left(\mathrm{solution}\right)+e^{-}\left(\mathrm{gas}\right)$. A method of determining absolute half-cell entropies is described. The relationship is discussed for single-ion entropies in solution. $\Delta S^0$ for the hydrogen electrode is provisionally recommended to be -66.6±1.4 J/K mole at 298 K, based on a previously recommended value for the absolute entropy of ${\mathrm{H}}^{+}$ in water. More accurate measurements should be attempted.