An Assessment of Reproduction of ΔrHo, ΔrCpo, ΔrVo for Water Ionization with Existing Formulations for the Ionization Constant of Water

Abstract

Two correlations for the ionization constant of water, log10 Kw, over extended temperature and pressure/density ranges have been proposed in the literature: the Marshall–Franck and Bandura–Lvov formulations. The question remains how well these correlations reproduce the experimental values of ΔrHo, ΔrCpo, and ΔrVo, i.e., the standard changes of the enthalpy, heat capacity, and volume of reaction of water ionization. The answer to this question is the main goal of this communication. First, the analytical expressions for calculating ΔrHo, ΔrCpo, and ΔrVo were derived for the Marshall–Franck and Bandura–Lvov models. Then the calculated values of ΔrHo, ΔrCpo, and ΔrVo were compared with the experimental results from the literature. Although the performance of both correlating models can be termed satisfactory, they do not reproduce existing ΔrHo, ΔrCpo, and ΔrVo data within their expected uncertainties, contrary to the situation with log10 Kw. On the other hand, it appears that the potential for the quantitative reproduction of ΔrHo, ΔrCpo, and ΔrVo exists. It is suggested that the ΔrHo, ΔrCpo, and ΔrVo data should be included in the dataset for the global fit of data when developing formulations for log10 Kw.