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 [yH₂O + (1 − y)C₆H₆](g) and [yH₂O + (1 − y)C₆H₁₂] (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 B₁₂ were extracted from the measurements by adjusting the interaction parameter ξ in the equation ε₁₂ = ξ(ε₁₁ε₂₂ )^1/2 for the cross-term potential-well depth. The B₁₂ values for water–cyclohexane are fitted by ξ = 0.94 but to fit the B₁₂ 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 B₁₂ 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.