Heat Capacities of Aqueous Solutions of Lithium Sulfate, Lithium Perchlorate, and Lithium Trifluoromethanesulfonate at 298.15 K

Abstract

Isobaric heat capacities of aqueous solutions of Li2SO4, LiClO4, and LiCF3SO3 have been measured at 298.15 K and 0.1 MPa up to high concentrations using a Picker flow calorimeter. Apparent molar isobaric heat capacities, Cp,ϕ, derived from these data were fitted within the limits of experimental precision with an extended Redlich–Rosenfeld–Meyer type of equation, which was also used to estimate the standard state (infinite dilution) quantities, Cp,ϕo, for each salt. The latter values were combined with appropriate literature data to produce a robust estimate of Cp,ϕo (Li+(aq)) = −3 ± 2 J·K–1·mol–1. Where comparison was possible, Cp,ϕ(LinX) values were closely parallel to those of the corresponding acids over the whole concentration range, even when the shapes of the curves were highly unusual. In contrast, Cp,ϕ(NanX) values always exhibited a crossover with the lithium salt data at a concentration of about 1 mol·kg–1, which appears to reflect differences in the hydration of the two cations.