Thermodynamic properties of the mixtures of a dioxanonane isomer + n-octane at 298.15 K : Part II. Excess molar volumes and excess isentropic and isothermal compressibilities (measurements of density and speed of sound)

Abstract

Densities, ϱ, and speeds of sound, u, of six mixtures of an isomer of the diethers 2, m- or 3, n-dioxanonane ( m = 5, 6, 7, 8; n = 6, 7) + n-octane were measured at 298.15 K. The densities provided excess molar volumes V E, and excess isothermal compressibilities, k T E, of the mixtures were estimated using heat capacities and isentropic compressibilities, k s e, obtained from measurements of density and speed of sound. The excess volumes were positive and parabolic, ranging from 0.5 to 0.7 cm 3 mol −1 and depending on both the density and dipole moment, μ, of the pure diethers. The excess isentropic compressibilities are positive and parabolic, except for the 2,8-dioxanonane + n-octane system, where the curve is flattened at large diether mole fractions and the maximum shifts to the small mole fractions. The excess isothermal compressibilities are almost parallel to the excess isentropic compressibilities but are about 20% higher. The speeds of sound, isentropic and isothermal compressibilities of the pure diethers are all very similar to each other and strongly correlated with their densities.