The contour of excess molar enthalpy at a mole fraction of benzene x = 0.548 on the p-T plane in liquid state and near the critical points for the (benzene + cyclohexane) mixture

Highlights: • The H^E_m of benzene + cyclohexane was measured near vapor pressure curve of benzene. • And was measured in the region between liquid state and state near critical points. • The contour of H^E_m was created on the p-T plane over a wide range of p and T. • Three-dimensional behavior of H^E_m are discussed. • H^E_m reached a local maximum at p and T slightly less than benzene critical point. The excess molar enthalpy H^E_m(x = 0.548) of the {x benzene + (1 − x) cyclohexane} mixture was measured near the vapour pressure curve of benzene, and was measured in the intermediate region between the liquid state and the state near the critical points. The contour of H^E_m(x = 0.548) was created on the p-T plane over a wide range of temperature and pressure including near the critical points. A valley was observed for the H^E_m(T, p, x = 0.548) surface in the intermediate region between the liquid state and the state near the critical points. The H^E_m(x = 0.548) smoothly decreased on the high-temperature side of the valley as temperature and pressure increased, and dramatically increased in this region as the temperature and pressure approached the critical points. Near these critical points, the H^E_m(T, p, x = 0.548) surface had two ridges, which extended the vapour pressure curves of benzene and cyclohexane. Finally, it was observed that near the critical point of benzene, H^E_m(x = 0.548) reached a local maximum at a temperature and pressure slightly less than the critical point of benzene.