The enthalpy of dilution of o-terphenyl in benzene and the temperature dependence of interaction parameters

Abstract

Enthalpies of dilution of o-terphenyl in benzene were measured calorimetrically at 288.15, 293.15, 298.15, 303.15, and 308.15 K. In the range of the volume fraction near the solubilities to high dilutions, φ 2 ≈ 0.7 to 0.04, enthalpies of dilution observed are all positive. The enthalpy parameter χ H and its dependence on volume fraction calculated from experimental results are reproduced by the linear functions: 0.091 1−0.01 0 φ 2 , 0.079 9+0.007 4 φ 2 , 0.068 5+0.003 6 φ 2 , 0.062 4 + 0.005 4, φ 2 , and 0.056 8−0.002 2 φ 2 , respectively at 288.15, 293.15, 298.15, 303.15, and 308.15 K, where φ 2 is a volume fraction of o-terphenyl. These observations show that χ H decreases with rise of temperature. A comparison of χ H among the isomers at 298.15 K show that the relative order of energetic affinity for benzene in solution is ortho- > meta- > para-terphenyls.