Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The pressure dependences of excess molar enthalpies HE m of the (benzene + cyclohexane) mixture at constant temperatures and compositions were measured near the critical locus, using a twin flow type mixing calorimeter. The measurement states are as follows; temperature T = (558.2, 563.2, and 573.2) K, mole fraction of benzene x = (0.119 to 0.916), and pressure range p = (3 to 15) MPa. The composition dependences of HE m at constant pressures and at each temperature were calculated from the pressure dependences of HE m. All pressure dependences of HE m have two peaks except at x = 0.916. The pressure dependences at x = 0.916 have one peak, and the curve at T = 573.2 K has a shoulder near p = 5 MPa. From the detailed consideration with respect to the phase behaviour near the critical locus for this mixture, two peaks should exist in the pressure dependences of HE m at T = 558.2 K and x = 0.916, but the second peak cannot be detected because the peak width is too narrow. The composition dependences of HE m near the critical locus were skewed or S-shaped ones, which are ascribed as the characteristic behaviour in the vicinity of the critical locus.