Compressions of (water + formamide or N, N-dimethylformamide) at pressures up to 150 MPa and at the temperature 298.15 K

Abstract

Compressions k of (water + formamide or N, N-dimethylformamide) were measured over the whole mole-fraction range at pressures up to 150 MPa and at the temperature 298.15 K. The experimental compressions for each mixture were fitted to the Tait equation. Isothermal compressibilities κT for the mixtures at a given pressure are evaluated from the Tait parameters. The composition dependence of k and κT values obtained for each aqueous amide mixture shows a similar behaviour at each pressure. Excess molar volumes VEm at high pressures are calculated from the compressions in combination with the reported densities at the pressure 0.1 MPa. Partial molar volumes Vi of the components i for both aqueous mixtures at a given pressure and their pressure derivative (∂Vi/∂p)T at the pressure 0.1 MPa are evaluated as a function of mole fraction. For aqueous N, N-dimethylformamide, the composition dependence of (∂Vi/∂p)T is compared with that of (∂Vi/∂p)S found in the literature. The changes in the excess molar Gibbs energy ΔGEm(p) at each pressure are evaluated from the pressure dependence of the VEm values. Pressure dependence of ΔGEm(p) for (0.5H2O + 0.5HCONR2) and for other aqueous organic mixtures is compared. The above thermodynamic properties are discussed from the viewpoint of molecular interaction between water and amide molecules.