Isotope effects on thermodynamic properties: mixtures of x(D 2O or H 2O) + (1 − x)CH 3CN at 298.15 K

Abstract

Excess molar enthalpies, excess isobaric molar heat capacities, densities and speeds of sound of the mixtures x(H 2O or D 2O) + (1 − x)CH 3CN were measured at 298.15 K. Considerable isotope effects were observed in H E m, V E m, C E p,m C E V,m , κ E S, and κ E T. D 2O + CH 3CN mixture was more positive for the positive excess properties and more negative for the negative ones than those for the H 2O + CH 3CN mixture. This can be ascribed to the stronger hydrogen bonds of D 2O water than H 2O water. Excess properties of both mixtures are very similar to each other. H E m values are positive except for the region x > 0.97, where they show a small negative value. C E p,m values are very large and positive, and the trend to more positive values makes an anomalous hump in the region x > 0.8, which corresponds to the negative part of H E m C E V,m values are smaller than those of C E p,m and resemble them. V E m, κ E S and κ E T values are negative for the whole concentration range.