A thermodynamical investigation of the system benzene-diphenyl

Abstract

The partial molar heat content, entropy and free energy of benzene in solutions of diphenyl in benzene have been determined by measurement of the partial pressures of benzene over the solu-­ tions. The whole composition range has been covered (as far as the solubility of diphenyl will allow), at temperatures from 30 to 80° C. A check on the accuracy of the experimental method has been made by measuring the vapour pressure of pure benzene over this temperature range, and good agreement has been found with recent values reported in the literature. The calculation of the thermodynamic functions from the vapour pressures requires a knowledge of the compressibility of benzene vapour. An experimental method has been devised for determining the gas imperfections of vapours, and using this the second and third virial coefficients of benzene vapour at various temperatures have been obtained. The variation of the thermodynamic functions of benzene with the composition of the solutions has been compared with that to be expected on the basis of recent statistical theories. It is found that whereas the non-ideal partial molar free energy can be accounted for almost exactly by the theo­ retical expression, the separate heat contents and entropies show some deviations. It is suggested that these deviations arise from slight changes in molecular packing as the composition is varied. The activities of benzene and diphenyl in saturated solutions at 30 to 60° C have been obtained from the vapour pressures of saturated solutions at these temperatures. These lead to values for the latent heat of fusion of diphenyl in agreement with the calorimetric value. The yapour pressure of saturated solutions is discussed.