Low temperature heat capacities and standard molar enthalpy of formation of sodium benzoate C6H5COONa (s)

Sodium benzoate was synthesized by the method of liquid phase synthesis, in which benzoic acid and anhydrous sodium carbonate were chosen as the reactants. The structure and composition of the compound were characterized by FTIR, chemical analysis, elemental analysis and X-ray powder diffraction techniques. Low temperature heat capacities of the compound were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 400 K. A polynomial equation of the heat capacities as a function of the temperature was fitted by least square method. The smoothed heat capacities and the thermodynamic functions of the compound relative to 298.15 K have been calculated based on the equation. In accordance with Hess law, the standard molar enthalpy of formation of the title compound C6H5COONa (s) was determined to be ΔfH°m[C6H5COONa,s]=−(642.56±0.64) kJ mol−1 by using an isoperibol solution-reaction calorimeter.