Excess partial molar enthalpies of { xH 2O + (1 − x)D 2O} at and below 298.15 K

Abstract

The excess partial molar enthalpies H m E(H 2O) and H m E(D 2O) in { xH 2O + (1 − x)D 2O} were measured at 298.15 K in the range 0.0107 < x < 0.9954. The purpose of the present measurements was to see whether a subtle difference in the nature of the hydrogen-bond network between H 2O and D 2O manifested itself in differences between the excess partial molar enthalpies. It turned out that in the range of measurement, these values were identical within the experimental uncertainty, ±0.3 J·mol −1, and were expressed as H m E(H 2O) = A 1(1 − x) 2 and H m E(H 2O) = A 1 x 2, with A 1 = 132.3 J·mol −1 at 298.15 K. It may therefore be necessary to cover the range x < 0.0107 and x > 0.9954 before any difference in H m E(H 2O) and H m E(D 2O) can be detected. The excess molar enthalpies H m E were thén calculated from the excess partial molar enthalpies as H m E = A 1 x(1 − x). The values of the latter agreed with the existing literature values to within ±2 J·mol −1. A smaller number of measurements were also made at 284.34, 277.17, and 277.13 K. By using the same expression as for 298.15 K, the values of A 1 were found to be 130.1 J·mol −1 at 284.34 K, 131.9 J·mol −1 at 277.17 K, and 130.8 J·mol −1 at 277.13 K. These values have larger uncertainties than at 298.15 K.