Traceable Thermodynamic Quantities for Dilute Aqueous Sodium Chloride Solutions at Temperatures from (0 to 80) °C. Part 2. The Quantities Associated with the Partial Molar Heat Capacity

Abstract

In Part 1 of this two-part study (J. Chem. Eng. Data 2017, 62, 2617–2632), we presented fully traceable two-parameter Hückel equations (with parameters B and b1) for the activity and osmotic coefficients in dilute aqueous NaCl solutions in the temperature range (0 to 80) °C, and these equations apply within experimental error to almost all thermodynamic data existing in the literature and used in the tests at least up to a molality of 0.2 mol·kg–1. These data include also molar enthalpies of the components in the solutions. In our model, parameter B is treated as a constant whereas parameter b1 depends in a quadratic way on the temperature. No calorimetric data were used in the parameter estimation of the model. In this second part (Part 2) of the study, the results of the quantities associated with the heat capacity of NaCl solutions are considered. All heat capacity data available for NaCl solutions at least up to 0.2 mol·kg–1 can be predicted within experimental error using the same Hückel equations as those determined in Part 1 in dilute NaCl solutions from (0 to 80) °C. For comparison, also other parametrization (obtained in Part 1 for higher temperatures) was here considered and it applies better to less dilute solutions in the higher temperatures than the model recommended now primarily. Following the success of the new models, we supplement the thermodynamic tables of Part 1 with the relative apparent and partial molar hear capacities for NaCl solutions. We have good reason to believe that the new tables contain the most reliable values available for the heat capacity quantities in dilute NaCl solutions.