Thermodynamically Traceable Calorimetric Results for Aqueous Sodium Chloride Solutions from T = (273.15 to 373.15) K up to the Saturated Solutions: Part 2 —The Quantities Associated with the Partial Molar Heat Capacity

Abstract

In previous articles (Partanen and Partanen in J. Chem. Eng. Data 65: 5226 − 5239 (2020), J. Solution Chem. 52: 1352 − 1385 (2023)), we presented a traceable and transparent three-parameter model for thermodynamic activity and enthalpy quantities in aqueous NaCl solutions. The model is based on extended Hückel equations with parameters B, b₁, and b₂ and it applies from T = 273.15 to 373.15 K up to the saturated solutions. These studies demonstrate that the model explains the literature data of almost all thermodynamic quantities including apparent and partial molar enthalpies within experimental error. In the model, the ion-size parameter in the Debye–Hückel equation, B, is regarded as a constant while the parameters of the coefficients of the linear and quadratic molality terms, b₁ and b₂, respectively, possess quadratic temperature dependences. In this study, the results obtained for the heat capacity quantities of NaCl(aq) are considered. We show that the available heat capacity literature for these solutions can be predicted at least satisfactorily up to the saturated solutions with our new model. Following this success, we supplement the existing thermodynamic tables with the new values for the relative apparent and partial molar heat capacities for NaCl solutions. It is likely that the new tables contain the most reliable values determined so far even though no calorimetric data were used in the parameter estimation of our model.

Graphical Abstract