Thermodynamic Investigation of Electrolytes of the Vanadium Redox Flow Battery (V): Conductivity and Ionic Dissociation of Vanadyl Sulfate in Aqueous Solution in the 278.15–318.15 K Temperature Range

Abstract

Precise measurements of electrical conductivities of aqueous VOSO4 solutions at various molalities were performed from 278.15 to 318.15 K in 5 K intervals. In terms of Fuoss’s equation and Shedlovsky’s equation, the limiting molar conductance, Λ 0, and the dissociation constant, K d, of the ion-pair [VOSO4]0 were determined. From an empirical equation for the temperature dependence of dissociation constants, the thermodynamic functions for the dissociation process of the ion-pair [VOSO4]0 were calculated. It is discovered that the reaction for ion-pair dissociation is unfavorable under normal pressure and room temperature because the standard state dissociation Gibbs energy (ΔG 0) > 0. The calculated values of the dissociation entropy and the dissociation enthalpy are negative, indicating that the dissociation entropy opposes the dissociation process.