The heat capacities and thermodynamic functions of 4-methylbiphenyl and 4- tert-butylbiphenyl

Abstract

The heat capacities of 4-methylbiphenyl and 4- tert-butylbiphenyl were measured by vacuum adiabatic calorimetry over the temperature range from (8 to 372) K. The temperatures and changes of the enthalpy and entropy of the phase transitions have been determined. The saturation vapour pressures of the biphenyl derivatives were measured by the dynamic transpiration method over the temperature and pressure intervals from (301 to 362) K and (0.09 to 69.5) Pa, respectively. The enthalpies of vaporisation and sublimation at T = 298.15 K were derived. The standard thermodynamic functions (changes of the entropy, enthalpy, and Gibbs free energy) were obtained for the crystal and liquid states for the temperature intervals studied and for the ideal gas state at T = 298.15 K. The ideal gas entropies of the compounds under study were also calculated by the principle of additivity and the correlation equations of TRC data series of NIST. The S m 0 ( g ) ( 298 K ) values derived from the experimental and calculated data agree within (1 to 1.3)% that supports their reliability.