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

Abstract

A flow mixing calorimeter has been used to measure the excess molar enthalpy H E m of gaseous (water + acetone) at the mole fraction y=0.5, at standard atmospheric pressure, and over the temperature range 383.2 K to 443.2 K. The excess molar enthalpy is negative, indicating that the strength of the water–acetone hydrogen bond is greater than that of the water–water hydrogen bond. Information about the strength of the water–acetone hydrogen bond 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–acetone hydrogen bond was found to be ΔH 12=−(20.2±2) kJ· mol −1 and K 12 (298.15 K)=1.256 MPa −1 .