Application of the Kirkwood-Buff theory of solutions to acetonitrile plus amide binary mixtures by using inversion procedure and regular solution theory

The Kirkwood-Buff (K-B) integrals play an important role in characterizing the intermolecular interactions in liquid mixtures. These are represented by the K-B parameters, G(AA), G(BB), and G(AB), which reflect correlation between like-like and like-unlike species in the mixture. The K-B integrals of binary mixtures of acetonitrile (ACN) with formamide (FA), N,N-dimethylformamide (DMF), N-methylacetamide (NMA) and N,N-dimethylacetamide (DMA) at 298.15 K and at atmospheric pressure have been computed from the experimental data of ultrasonic speed and density. We have used the similar inverse procedure (as proposed by Ben-Naim) to compute the K-B Parameters of the mixtures, in which thermodynamic information on mixtures such as partial molar volumes, isothermal compressibility, and experimental data of partial vapour pressures are used. A new route has been incorporated by using regular Solution theory in the computation of excess free energy for obtaining the partial vapour pressures of binary liquid mixtures. The low values of excess entropy (S(E) approximate to 0) obtained for these mixtures indicate the applicability of regular solution theory to these mixtures. The results obtained regarding intermolecular interaction in all the four Mixtures under study from this new procedure are in good agreement with those obtained from the trends exhibited by the excess functions of these mixtures.