Ultrasound Speeds and Molar Isentropic Compressions of Aqueous Binary Mixtures of Diethylamine from 278.15 to 308.15 K

Ultrasound speeds in aqueous binary mixtures of diethylamine (DEA) were measured across the entire composition range at five temperatures between 278.15 and 308.15 K. Isentropic compressibilities, κS, were calculated from the ultrasound speed and density data. The excess molar isentropic compressions, KS,mE, were estimated and their variation with the mole fraction of the amine were fitted by the Redlich–Kister equation. Excess partial molar isentropic compressions, KS,iE, were then obtained, allowing separation of the role of each component in the mixing process. Interesting insights are gained from the analysis of the temperature and composition dependence of KS,iE, principally in the water-rich region. A comparison of the limiting values of this property with those of the limiting excess partial molar isobaric expansion, EP,iE,∞, previously published, clearly shows the different sensitivity of these two differential thermodynamic properties to the mixing process. The different behavior of the temperature dependence of KS,iE,∞ in the systems, water + DEA, and water + 2-diethylaminoethanol (DEEA), are also analyzed and interpreted in terms of changes in the solute configuration, the degree of hydrolysis and solute-solvent interactions.