Thermodynamically Traceable Calorimetric Results for Dilute Aqueous Potassium Chloride Solutions at Temperatures from 273.15 to 373.15 K. Part 2. The Quantities Associated with the Partial Molar Heat Capacity

Jaakko I Partanen,Kari P Vahteristo,Lauri J Partanen

doi:10.1021/acs.jced.9b00373

Abstract

In previous articles (Partanen J. Chem. Eng. Data 2019, 64, 16−33 and Partanen J. Chem. Eng. Data 2019, 64, 2519–2535), we presented traceable and transparent two-parameter Hückel equations (with parameters B and b1) for the activity coefficients of the salt and for the osmotic coefficients of water in aqueous KCl solutions in the temperature range of 273.15–383.15 K. The latter article is the first part (Part 1) of the calorimetric study. We showed in these articles that our equations for these solutions explain within experimental error the literature data on almost all thermodynamic quantities including the partial molar enthalpies at least up to a molality of 0.2 mol·kg–1 and up to 373 K. In this model, parameter B is regarded as a constant but parameter b1 has a quadratic temperature dependence. No calorimetric data were needed in the parameter estimation. In the second part (Part 2) of the calorimetric study, now, the results obtained for the heat capacity quantities of KCl (aq.) are considered. We show here that all heat capacity literature available for KCl solutions at least up to 0.5 mol·kg–1 is possible to explain within experimental error using exactly the same Hückel equations as those considered previously in our studies for dilute KCl solutions from 273 to 373 K. Because of the success of the used model, we supplement the existing thermodynamic tables with new values for the relative apparent and partial molar heat capacities for KCl solutions. It is likely that the new tables contain the most reliable values available for these heat capacity quantities.

Highlights

Due to its central role in biological and industrial systems, potassium chloride is without question one of the most important electrolytes on earth
In ref 5 and in Part 1 of this study,[11] we demonstrated that the Hückel equation with the two parameters, denoted B and b1, is the most accurate equation to date for predicting the thermodynamic properties of dilute KCl at various temperatures
Based on extensive testing against the existing activity and osmotic coefficient data,[5,12] high-quality enthalpy data,[11] and heat capacity data, we conclude that the measured results for dilute KCl solutions can often be predicted within their experimental uncertainty up to a molality of 1.0 mol· kg−1 in the temperature range 273−373 K with a simple reparametrization of the Hückel equation

Summary

Introduction

Due to its central role in biological and industrial systems, potassium chloride is without question one of the most important electrolytes on earth. As described in ref 4 for the NaCl case, the following simple strategy gave accurate and traceable results for the interpretation of the complicated heat capacity data existing in the literature for dilute KCl (aq.) at various temperatures at least up to 0.2 mol·kg−1: Using eq 3

Results

Conclusion