Synthesis, characterization, and thermodynamic study of ammonium benzoate C7H5O2NH4(s)

Benzoic acid and concentrated ammonia were chosen as reactants and a novel compound (ammonium benzoate) was synthesized using the method of liquid phase reaction. FTIR, elemental analysis and X-ray powder diffraction technique were applied to characterize the structure and composition of the compound. Low-temperature heat capacities of the solid compound were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 399 K. A polynomial equation of the heat capacities was fitted by the least-squares method. In accordance with Hess’ law, a thermochemical cycle was designed, the enthalpy change of the reaction of benzoic acid with ammonium acetate was determined as ΔrHm°=(15.59±0.50) kJ mol−1, and the standard molar enthalpy of formation of the compound was calculated as ΔfHm°   [C7H5O2NH4,s]=−(472.65±0.62) kJ mol−1 by an isoperibol solution–reaction calorimeter.