Excess acoustical and volumetric properties and the theoretical estimation of the excess thermodynamic functions of binary liquid mixtures

With the help of the measured ultrasonic velocity (u) and density (rho), the excess ultrasonic velocity (Delta u), excess acoustic impedance (Z(E)), and excess intermolecular free length (L-f(E)) have been calculated for two binary liquid mixtures of tetrahydrofuran (THF) with 1-propanol (1-P) and 2- propanol (2-P) at the temperatures 293, 303, and 313K over the entire mole fraction range and fitted to the Redlich- Kister polynomial equation. The excess ultrasonic velocity, excess acoustic impedance, and excess intermolecular free length were plotted against the mole fraction of THF over the whole mole composition range. The observed positive values of Delta u and Z(E) and the negative values of L-f(E) were explained on the basis of the intermolecular interactions present in these mixtures. The experimental results for the ultrasonic velocity and density were used to compute the thermodynamic excess functions, viz. the energy (E-E), molar volume (V-E), and entropy (S-E), for two binary liquid mixtures at varying temperatures. Flory's theory was also applied for evaluating the ultrasonic velocity using the Auerbach relation. A good agreement has been found between the experimental and calculated values of the ultrasonic velocity. The strength and the nature of the interactions between like and unlike molecules have been discussed.