Evidence for nonideality in liquid mixtures of hydrogen chloride and deuterium chloride

Abstract

of hydrogen chloride and deuterium chloride has been measured at nine temperatures between 195 and 226 K. The results show that the vapor pressure of this liquid mixture is greater than what would be expected if the solution were strictly ideal, by 72 Pa at 223.35 K and by 34 Pa at 200 K. These pressure differences are between 1 and 2 parts in lo4 of the vapor pressure. The nonideality is also illustrated by the fact that the temperature at which the vapor pressure of hydrogen chloride and that of the liquid mixture are equal is about 0.5 K lower than the temperature (223.35 K) at which pure hydrogen chloride and deuterium chloride have the same vapor pressure. It is difficult to assess what contribution to the nonideality is made by the imperfection of the vapor phase, but reasons are given for believing that the observed effects are primarily a manifestation of nonideality in the liquid phase. These effects correspond to an excess Gibbs energy (GE) for the equimolar mixture of about 0.25 J mol-] over the temperature range of the measurements, which is some 3 orders of magnitude smaller than the GE values typically found for mixtures of two (nonisotopic) condensed gases.