Interpolation of the Temperature Dependence of the Fusion Enthalpy of Aromatic Compounds Between 298.15 K and the Melting Temperature

Abstract

Knowledge of the fusion enthalpy as a function of temperature is necessary when performing rigorous thermodynamic calculations involving crystal-liquid transition. The fusion enthalpy can be measured directly only at the melting point (T_m). Derivation of its temperature dependence according to Kirchhoff’s law of Thermochemistry requires measuring the heat capacities of liquid and solid in a temperature range of interest, which is obstructed by fast crystallization of the liquids below the melting temperature. Another option is an extrapolation of the temperature dependence of the melt heat capacity. Its precise measurement in a wide range demands remarkable efforts, especially in the case of high-melting and thermally unstable compounds. In this work, we showed that the fusion enthalpy between 298.15 K and T_m can be estimated using two relatively simple experiments: solution calorimetry and conventional fusion enthalpy measurement at T_m. The fusion enthalpies interpolated as a linear function of temperature were compared with the values derived according to Kirchhoff’s law of Thermochemistry. An agreement within 1–2 kJ·mol⁻¹ was observed for the vast majority of compounds.