Thermodynamic properties of some nonelectrolytic solutions


Calorimetric heats of mixing per mole, ΔH_x^M, and a solid-liquid phase diagram were obtained for the system water--p-dioxane at 25°C over the entire range of composition. From these data are derived values for the partial molar heat contents, activities and free energies and entropies of mixing. The excess free energy-composition curve, which is roughly parabolic in shape, gives little indication of the extent of interaction in this system. The ΔH_x^M values, however, range from 115 cal./mole endothermic to 142 cal./mole exothermic. A sharp exothermic dip occurs at a mole fraction of 0.143, which corresponds to a ratio of 6.00 water molecules to each dioxane molecule. Minimum values for the freezing points and entropies of mixing also occur at approximately this same composition. Possible short range structures that could contribute to the properties of this system are discussed. ΔH_x^M data were determined calorimetrically for the ternary and the three binary systems that can be formed from carbon tetrachloride (1), cyclohexane (2), and benzene (3). The following analytical equations, in which x_i is the mole fraction of component i, summarize these data: ΔH_12^M = x_1x_2 [ 160.8 / 18.9 (x_1 - x_2) - 20.2(x_1 - x_2)^2 ] 15,25,and 35°c ΔH_13^M = x_1x_3 [ 103.2 / 11.0 (x_1 - x_3) - 13.3(x_1 - x_3)^2 ] 25°C ΔH_13^M = x_1x_3 [ 96 / 4.17 (x_1 - x_3) - 13.19 (x_1 - x_3)^2 ] 10°C ΔH_23^M = x_2x_3 [ 3105 - 7.980 T - (1303-4.370 T) (x_2 - x_3) / (1738 - 5.486 T) (x_2 - x_3)^2 ] 15,25,and 35°C ΔH_123^M = x_1x_2 [ 160.8 / 18.9 (x_1 - x_2) - 20.2 (x_1 - x_2)^2 ] / x_1x_3 [ 103.2 / 11.0 (x_1 - x_3) - 13.3 (x_1 - x_3)^2 ] / x_2x_3 [ 726.0 / 102.4 (x_2 - x_3)^2 ] 25°C Solid-liquid phase equilibria data were also obtained for these systems. This information for the system cyclohexane-benzene, together with the thermal data, made possible the calculation of the partial molar heat contents, L_i, and the excess free energies, ΔF_x^E, and entropies, ΔS_x^E, of mixing per mole as functions of composition. These data are summarized by the following expressions: L_2 = x_3^2 [ (6146 - 17.836T) - (19116-61.368T) x_2 / (20856-65.832T) x_2^2 ] L_3 = x_2^2 [ (3540-9,096T) - (8692-26.408T) x_3 / (20856-65.832T) x_3^2 ] ΔF_x^E = x_2x_3 [ 310.6 / 2.33 (x_2 - x_3) / 40.0 (x_2 - x_3)^2 / 130.8 (x_2 - x_3)^3 ] 25°C TΔS_x^E = x_2x_3 [ 415.4 - 2.33 (x_2 - x_3) / 62.4 (x_2 - x_3)^2 - 130.8 (x_2 - x_3)^3 ] 25°C The system carbon tetrachloride-benzene proved to be especially interesting in that the phase diagram of this "near-to-ideal" system reveals a complex of approximately one benzene molecule to one carbon tetrachloride molecule composition. It is suggested that TT bonding between the electron cloud of the aromatic ring and the empty 3-d shell of chlorine may be responsible for the formation of the compound. Replacing benzene with p-xylene to increase the electron density of the ring enhanced the formation of the complex. On the other hand, either decreasing the electron density of the ring by using nitrobenzene, or decreasing the electronegativity of the chlorine atoms by substituting CHCl_3 for CCl_4 prevented complex formation. The results of this study of carbon tetrachloride-cyclohexane-benzene mixtures seem to indicate that the system carbon tetrachloride-cyclohexane is very nearly ideal, the system carbon tetrachloride-benzene is much more complex than was previously considered, and the high entropy in the system cyolohexane-benzene is probably due partially to volume change on mixing and partially to lack of randomness in the pure benzene.



College and Department

Chemistry and Biochemistry



Date Submitted


Document Type





Carbon compounds, Thermodynamics



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