| Abstract |
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, kappa(S) , were calculated from the ultrasound speed and density data. The excess molar isentropic compressions, K (E)(S,m), were estimated and their variation with the mole fraction of the amine were fitted by the Redlich-Kister equation. Excess partial molar isentropic compressions, K (E)(S,i), 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 K (E)(S,i), 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, E-P,i(E,infinity), 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 K (E,infinity)(S,i) 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. |
