Benzene–water association Excess molar enthalpy and second virial cross-coefficients for (benzene–water)(g) and (cyclohexane–water)(g)

Abstract

New measurements of the excess molar enthalpy H _m ^E of [yH ₂ O + (1 − y)C ₆ H ₆ ](g) and [yH ₂ O + (1 − y)C ₆ H ₁₂ ] (g) measured at standard atmospheric pressure over the temperature range 403.15 to 433.15 K and for y = 0.5 are reported. These measurements supplement earlier measurements at standard atmospheric pressure over the range 363.15 to 393.15 K. High-pressure H _m ^E measurements reported previously have been extrapolated to yield further values of H _m ^E at standard atmospheric pressure over the range 498.2 to 698.2 K. Second virial coefficients for the hydrocarbons were fitted by the Kihara potential, and the Stockmayer potential was used for water in its interaction with hydrocarbon. Second virial cross-coefficients B ₁₂ were extracted from the measurements by adjusting the interaction parameter ξ in the equation ε ₁₂ = ξ(ε ₁₁ ε ₂₂ ) ^1/2 for the cross-term potential-well depth. The B ₁₂ values for water–cyclohexane are fitted by ξ = 0.94 but to fit the B ₁₂ values for water–benzene a value of ξ = 1.27 is needed. This high value is an indicator of the strength of the specific interaction between water and benzene. Analysis of the B ₁₂ values using an association model shows that the enthalpy of the specific interaction between benzene and water is −(11.3 + 2) kJ mol ⁻¹ , approximately half the energy of the specific interaction between two water molecules.