Water–sulphur dioxide association. Second virial cross coefficients for water–sulphur dioxide derived 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 + sulphur dioxide) at the mole fraction y=0.5, at standard atmospheric pressure, and over the temperature range (383.2 to 483.2 K). Information about the strength of the water–sulphur dioxide 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. 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–sulphur dioxide interaction was found to be ΔH 12=−(14.9±2) kJ· mol −1 , and K 12(298.15 K)=0.18 MPa −1 . Values of the second virial cross coefficient are fitted by the equation B 12/(cm 3·mol −1)=29.6−39290·(K/ T)−3.0973·exp{1493·(K/ T)}.