Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

A twin flow type of mixing calorimeter was constructed for measuring excess enthalpies of fluid mixtures over wide temperature and pressure ranges. The precision of the calorimeter was tested with (water + ethanol) mixture. The excess molar enthalpies HE m for the (water + ethanol) mixture at temperatures T = (423.2 and 523.2) K and pressure p = 5.00 MPa and at T = 523.2 K and p = 15.00 MPa are in good agreement with the literature values. The HE m values for the (benzene + cyclohexane) mixture were measured using this calorimeter over the temperature range from T = 298.2 K to T = 573.2 K and the pressure range from p = 5.00 MPa to p = 25.00 MPa. All HE m values are positive and all mole fraction dependencies of HE m are almost symmetrically parabolic. The maximum values of the mole fraction dependence of HE m decrease with increasing temperature and are independent of the pressure, except for the conditions at T = (498.2 and 523.2) K and p = 5.00 MPa whose states are near the critical point of benzene. The maximum values of HE m of these states were greater than the values expected from the curve representing the temperature dependence of other maximum values of the mole fraction dependence of HE m.