关键词: 烟酸, 绝热量热法, 低温热容, 氧弹燃烧量热法, 标准摩尔生成焓

Low-temperature heat capacities of nicotinic acid (C₆H₅NO₂) 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 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 at the interval of 5 K. The constant-volume energy of combustion of nicotinic acid at T＝298.15 K was measured by a precision oxygen-bomb combustion calorimeter to be Δ_cU＝－(24528.3±16.1) J•g^－1. The standard molar enthalpy of combustion for the compound was determined to beΔ_cH_m^o＝－(3019.05±1.98) kJ•mol^－1, according to the definition of the combustion heat. Finally, the standard molar enthalpy of formation for the compound was determined to beΔ_fH_m^o＝－(56.76±2.13) kJ•mol^－1, in accordance with Hess law.

Key words: nicotinic acid, adiabatic calorimetry, low-temperature heat capacity, oxygen-bomb combustion calorimetry, standard molar enthalpy of formation