Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

A constant-volume piezometer immersed in a precision thermostat was used to measure the (p, v,T,x) relationship of three aqueous ethanol mixtures (0.2, 0.5, and 0.8) mole fraction of ethanol in the temperature range from (423.15 to 673.15) K, and at pressures between (0.9 and 51) MPa. This range includes the near-critical and supercritical regions. The measurements were performed in both one- and two-phase regions including the (vapour + liquid) coexistence curve. The total uncertainty of measurements of density, 0.15%, pressure, 0.05%, temperature, 15 mK, and composition, 0.05%. Isochoric and isothermal intersections with the phase boundary were performed to obtain the values of bubble and dew point pressures and densities. The values of the critical parameters (TC, pC, and qC) were extracted from the measured (p, v,T,x) relations in the critical region. Excess V E m, apparent /V, and partial V12 molar volumes were derived using the measured values of density for the mixtures and pure components data. For the water s critical isotherm-isochore (T = 647.1 K and 322.0 kg Ae m 3), the measurements were performed for very dilute mixtures to estimate accurately the values of the Krichevskii parameter. The value of the Krichevskii parameter was also calculated by using the critical-curves data for the mixture and vapour pressure data for the pure solvent (H2O). The derived value of the Krichevskii parameter was used to analyze the critical behaviour of the thermodynamic and structural properties of the (H2O+C2H5OH) mixture in terms of the principle of isomorphism of critical phenomena in binary mixtures. The values of the characteristic parameters (K1,K2), temperatures (s1, s2), and the characteristic density differences (Dq1,Dq2) were estimated for the (H2O+C2H5OH) mixture by using the critical-curve data and the theory of isomorphism of the critical phenomena in binary mixtures.