Molar heat capacity at constant volume of binary mixtures of 1,2-dibromo- and 1,2-dichloroethane with benzene

Abstract

The volume change of mixing and the thermal expansion coefficients of the systems benzene + dibromoethane, and benzene + dichloroethane, and the ultrasonic sound velocity of the latter system, have been determined over the entire concentration range. From these values, and from data for the heat capacity at constant pressure C_p, the isothermal compressibility χ_T, the adiabatic compressibility χ_s, and the molar heat capacity at constant volume C_v of the two systems have been calculated. For benzene + dichloroethane, C_v is slightly greater than the value calculated by assuming that the heat capacity is additive on a mole fraction basis and this can be explained by a change of the transgauche conformational equilibrium of dichloroethane. For benzene + dibromoethane, C_v shows negative deviations from additivity. The assumption that this is due to an enhancement of rotational freedom of the molecules is discussed from the point of view of the cell model for non-electrolytic mixtures.