RECONCILIATION OF CALORIMETRICALLY AND SPECTROSCOPICALLY DERIVED THERMODYNAMIC PROPERTIES AT PRESSURES GREATER-THAN 0.1 MPA FOR BENZENE AND METHYLBENZENE - THE IMPORTANCE OF THE 3RD VIRIAL-COEFFICIENT

Heat capacities for the liquid phase (to within 25 K of T(c)) and the critical temperature for benzene and methylbenzene were determined by differential-scanning calorimetry (dsc). The critical pressures were derived by a fitting procedure involving measured vapor pressures, densities, and the dsc results. The critical densities were estimated with a corresponding states correlation. Good agreement with reliable critical properties from the literature is shown. New measurements of vapor pressures for methylbenzene (305-422 K; 5.3-270.0 kPa) by comparative ebulliometry are reported. New density measurements for benzene (310-523 K) and methylbenzene (303-428 K) are reported also. The results were combined with literature entropies for the liquid to calculate ideal-gas entropies to near the respective critical temperatures. Validation of the results was accomplished by comparison with reliable ideal-gas entropies based on molecular spectroscopy and statistical mechanics. The significance of the third virial coefficient in the calorimetric calculations is demonstrated.