Measurements of the Heat Capacity of an Azeotropic Mixture of Water and n-Butanol from 78 to 320 K

Molar heat capacities of n‐butanol and the azeotropic mixture in the binary system [water (x=0.716) plus n‐butanol (x=0.284)] were measured with an adiabatic calorimeter in a temperature range from 78 to 320 K. The functions of the heat capacity with respect to thermodynamic temperature were established for the azeotropic mixture. A glass transition was observed at (111.9±1.2) K. The phase transitions took place at (179.26±0.77) and (269.69±0.14) K corresponding to the solid‐liquid phase transitions of n‐butanol and water, respectively. The phase‐transition enthalpy and entropy of water were calculated. A thermodynamic function of excess molar heat capacity with respect to temperature was established, which took account of physical mixing, destructions of self‐association and cross‐association for n‐butanol and water, respectively. The thermodynamic functions and the excess thermodynamic ones of the binary systems relative to 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity and the calculated excess heat capacity with respect to temperature.