Water–hydrogen chloride association. Second virial cross coefficients for water–hydrogen chloride from gas phase excess enthalpy measurements

Abstract

A flow mixing calorimeter has been used to measure the excess molar enthalpy H m E of gaseous (water + hydrogen chloride) at the mole fraction y=0.5, at standard atmospheric pressure, and over the temperature range 383.15 K to 483.15 K. Information about the strength of the water–hydrogen chloride interaction was obtained by analysing the measurements using a quasi-chemical association model. The second virial coefficient B 11 of water was written B 11= B ns 11− RTK 11. The non-specific interaction B ns 11 between water molecules was calculated from the Stockmayer potential with parameters appropriate to a water–nonpolar fluid interaction, and the specific (hydrogen bonding) forces were described by the association model in terms of an equilibrium constant K 11(298.15 K) = 0.36 MPa −1 and an enthalpy of formation of ΔH 11=−(16.2±2) kJ· mol −1 for the water–water hydrogen bond. Similarly for hydrogen chloride K 22(298.15 K)=0.026 and ΔH 22=−8.3 kJ· mol −1 . The second virial cross coefficient was written B 12= B 12 ns−( RTK 12)/2, and from the temperature dependence of ln K 12 the enthalpy of formation of the water–hydrogen chloride interaction was found to be ΔH 12=−(13.4±2) kJ· mol −1 , and K 12(298.15 K) = 0.42 MPa −1. Values of the second virial cross coefficient are fitted by the equation B 12/( cm 3· mol −1)=18 – 18922·( K/T)−9.8415· exp{1216·( K/T)} .