Synthesis, Characterization, and Thermodynamic Study of Barium Benzoate Ba(C7H5O2)2(s)

Abstract

Benzoic acid and barium hydroxide octahydrate were used as reactants, and a compound Ba(C7H5O2)2(s) was synthesized by the method of hydrothermal reaction. Chemical and elemental analyses, FTIR, and X-ray powder diffraction techniques were applied to characterize the composition and structure of the compound. Low-temperature heat capacities of the compound were measured by a precision automated adiabatic calorimeter over the temperature range from (77 to 402) K. A polynomial equation of the heat capacities as a function of temperature was fitted by the least-squares method. Smoothed heat capacities and thermodynamic functions of the compound were calculated on the basis of the fitted polynomial. The enthalpy change of the reaction of benzoic acid with barium hydroxide octahydrate was determined to be (22.03 ± 0.30) kJ·mol−1 by respective measuring enthalpies of dissolution of benzoic acid and Ba(C7H5O2)2(s) in 0.1 mol·dm−3 HCl and barium hydroxide octahydrate in 0.1 mol·dm−3 HCl solution containing certain amounts of benzoic acid at 298.15 K by using an isoperibol solution−reaction calorimeter. The standard molar enthalpy of formation of the title compound Ba(C7H5O2)2(s) was derived to be −(1231.47 ± 1.12) kJ·mol−1 in accordance with Hess’ law.