关键词: 无水烟酸锂, 绝热量热法, 低温热容, 等温环境溶解-反应量热法, 标准摩尔生成焓

Nicotinic acid and lithium hydroxide monohydrate were chosen as the reactants, anhydrous lithium nicotinate was synthesized by the method of hydrothermal synthesis. FTIR and X-ray powder diffraction techniques were applied to characterize its structure. Low-temperature heat capacities of the Li(C6H4NO2)(s) were measured with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 400 K. A polynomial equation of the heat capacities as a function of temperature was fitted by the least square method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated and tabulated at intervals of 5 K. A reasonable thermochemical cycle was designed, and the standard molar enthalpies of dissolution for the reactants and products of the reaction in the selected solvent were measured by an isoperibol solution-reaction calorimeter, respectively. In addition, the enthalpy change of the reaction was calculated to be ＝－(20.21±0.41) kJ•mol－1 from the data of the above standard molar enthalpies of dissolution. Finally, the standard molar enthalpy of formation of anhydrous lithium nicotinate Li(C6H4NO2)(s) was determined to be [Li(C6H4NO2), s]＝－(278.29±1.01) kJ•mol－1 in accordance with Hess law.

Key words: anhydrous lithium nicotinate, adiabatic calorimetry, low-temperature heat capacity, isoperibol solution-reaction calorimetry, standard molar enthalpy of formation