Benzene–dimethyl ketone association Excess molar enthalpy of (cyclohexane + dimethyl ketone)(g) and (benzene + dimethyl ketone)(g) from temperatures of 353.2 to 403.2 K

Abstract

A differential flow mixing calorimeter has been used to measure the excess molar enthalpy H_m^E of (cyclohexane + dimethyl ketone)(g) and (benzene + dimethyl ketone)(g) at standard atmospheric pressure over the temperature range 353.2–403.2 K. The non-ideality of the cyclohexane and benzene was fitted using the Kihara potential, and that of the dimethyl ketone using the Stockmayer potential. Cross terms were calculated using the equation ε₁₂ = (1 − k₁₂)(ε₁₁ε₂₂)^1/2 and to fit the measurements on (cyclohexane + dimethyl ketone)(g) the value (1 − k₁₂) = 1.175 was needed. None of the usual combining rules give this value.

The measurements on (benzene + dimethyl ketone)(g) could not be fitted by adjusting the value of (1 − k₁₂), though an approximate fit could be obtained using the value 1.38. The difference between the experimental values of H_m^E for (benzene + dimethyl ketone)(g) and those calculated using (1 − k₁₂) = 1.175, the value appropriate to (cyclohexane + dimethyl ketone)(g), was described in terms of a quasi-chemical model, which, for the benzene–dimethyl ketone interaction, yielded a value of the equilibrium constant K₁₂(298.15 K) = 0.349 MPa⁻¹ and an enthalpy of association ΔH₁₂ = −(16.4 ± 2) kJ mol⁻¹ . This value of ΔH is attributed to a charge transfer interaction between the benzene and dimethyl ketone molecules which is not present in the cyclohexane–dimethyl ketone interaction.