Heat capacity and thermochemical study of trifluoroacetamide (C2H2F3NO)

The low-temperature heat capacities of trifluoroacetamide were precisely determined with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 404 K. A solid-to-solid phase transition, a fusion and a phase transition from a liquid crystalline phase to fully liquid phase have been observed at the temperatures of 336.911±0.102, 347.622±0.094 and 388.896±0.160 K, respectively. The molar enthalpies of these phase transitions as well as the chemical purity of the substance were determined to be 5.576±0.004, 11.496±0.007, 1.340±0.005 kJ mol−1 and 99.30 mol%, respectively, on the basis of the heat capacity measurements. The molar entropies of the three phase transitions were calculated to be 16.550±0.012, 33.071±0.029 and 3.447±0.027 J mo1−1 K−1, respectively. Further researches of the thermochemical properties for this compound have been carried out by means of TG and DSC techniques.