Isobaric thermal expansivity and thermophysical characterization of liquids and liquid mixtures

A methodology for the thermophysical characterization of liquids and liquid mixtures based on measurements of density, sound speed and isobaric heat c apacity per unit volume at atmospheric pressure as a function of temperatur e is proposed. Density and sound speed data are used to determine the isent ropic compressibility from the Laplace equation. The precision in density m easurements allows one to obtain the isobaric thermal expansivity at differ ent temperatures using an incremental procedure with quite acceptable accur acy and precision. The isothermal compressibility and isochoric molar heat capacity are both obtained from the previous properties, using well-known t hermodynamic relations. The accuracy of the proposed methodology was checke d by determining the above-mentioned properties for liquid n-hexane, n-hept ane, n-octane, n-dodecane, n-hexadecane, cyclohexane, and toluene over the temperature range (288.15-333.15) K and comparing the results with selected reported data. The average absolute deviations from the latter showed data obtained with the proposed methodology to be reasonably accurate. The exce ss quantities for nine binary mixtures of the cyclohexane + n-dodecane syst em were also determined with a view to assessing precision, which was found to be quite good as regards the dependence on both composition and tempera ture.