Thermodynamic Functions of the Thiophene−Benzene System in Their Liquid and Solid Solutions

Abstract

The heat capacity of a new sample of thiophene−benzene, 0.182C4H4S + 0.818C6H6, was measured in order to complete a systematic thermodynamic study on the binary system. The measurement was carried out by using an adiabatic calorimeter with intermittent heating mode in the temperature range 13 and 300 K. Standard thermodynamic functions were calculated from the experimental data extrapolated to 0 K. Combining the results with those for other compositions already measured, a phase diagram of this binary system was drawn as functions of temperature and composition. In order to determine the excess thermodynamic quantities associated with mixing in the liquid state, the vapor pressure and enthalpy of mixing were measured at 298.15 K over the entire composition range. It turned out that the liquid solution behaved almost like the ideal solution. By a unique way, these data were combined with the standard thermodynamic functions of the solid and liquid phases to derive the excess thermodynamic functions for the solid solution. The liquidus and solidus curves observed experimentally were analyzed to derive the excess quantities at the equal-G temperature for the melting equilibria. A large nonideality of the solid solution turned out to be responsible for the deviation of the fusion curves from the ideal behavior. The residual entropy of the binary system was similarly determined. A substantial fraction of the residual entropy is considered to be due to freezing of the positional disorder of both components in the solid solution.