A thermodynamic study of aqueous acetonitrile: excess chemical potentials, partial molar enthalpies, entropies and volumes, and fluctuations

We measured vapour pressures of aqueous acetonitrile (abbreviated as ACN) at 6, 20, and 37 degreesC, from which excess chemical potentials of ACN (mu (E)(ACN)) were calculated. We also determined excess partial molar enthalpies of ACN (H-ACN(E)) at 6, 20, 30, 37, and 45 degreesC. From these data, excess partial molar entropies of ACN (S-ACN(E)) were calculated at 6, 20, and 37 degreesC. Using density data by Benson’s group, excess partial molar volumes of ACN (V-ACN(E)) were evaluated. The response function data by the same group were also used to evaluate amplitude and wavelength of mean-square fluctuations in terms of volume, entropy, and cross between volume and entropy. All the above quantities and their dependence on the mol fraction of solute, i.e., the effect of additional solute on the above quantities were used to study the effect of acetonitrile on the molecular organization of H2O. It was found that acetonitrile works as a stronger structure-making solute than methanol. Rather its effect on H2O is about the same as that of propan-1-ol.