关键词: 烟酸钠, 绝热量热法, 低温热容, 溶解-反应量热法, 标准摩尔生成焓

Abstract: Nicotinic acid and sodium acetate were chosen as the reactants, a compoundsodium nicotinate was synthesized by the method of room temperature solid phase synthesis. FTIR and X-ray powder diffraction technique were applied to characterize its structure, and its composition was determined to be Na(C₆H₄NO₂) by chemical and elemental analyses. Low-temperature heat capacities of the compound were measured by a precision automated adiabatic calorimeter over the temperature range from 78 K to 400 K. A polynomial equation of the heat capacities as a function of the temperature was fitted by the least square method. On the basis of the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated at the interval of 5 K. A reasonable thermochemical cycle was designed on the basis of the solid phase preparation reaction of the substance, 1 mol/L NaOH solution was chosen as the calorimetric solvent, and the standard molar enthalpies of dissolution for the reactants and products of the solid phase reaction in the selected solvents were measured by an isoperibol solution-reaction calorimeter, respectively. In addition, the enthalpy change of the solid phase reaction was determined to be (23.232±0.509) kJ/mol from the data of the above standard molar enthalpies of dissolution. Eventually, the standard molar enthalpy of formation of sodium nicotinate was derived to be: Δ_fH_m⁰[Na(C₆H₄NO₂), s]=(-548.96±1.11) kJ/mol, by the combination of the enthalpy change of the solid phase reaction with other auxiliary thermodynamic quantities.

Key words: Sodium nicotinate, Adiabatic calorimetry, Low-temperature heat capacity, Solution-reaction calorimetry, Standard molar enthalpy of formation