关键词: 乙二胺盐酸盐; 晶体结构; 低温热容; 标准摩尔溶解焓; 标准摩尔生成焓

Abstract:

Ethylene diamine dihydrochloride was synthesized by solvothermal synthesis. X-ray crystallography was applied to characterize its structure. Low-temperature heat capacities of the title compound were measured by a precision automated adiabatic calorimeter over the temperature range from 78 K to 370 K. A polynomial equation of heat capacities as a function of the temperature was fitted by least square method. A reasonable thermochemical cycle was designed on the basis of a designed thermochemical reaction(1.0 mol/L NaOH solution was chosen as the calorimetric solvent), and 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. Eventually, the standard molar enthalpy of formation of the title compound was derived to be -(540.74±1.33) kJ/mol by the Hess thermochemical cycle. The reliability of the designed thermochemical cycle was verified by UV-Vis spectroscopy and the data of the refractive indices. The standard molar enthalpy of formation of the title compound is negative with a larger absolute value. The results show that the title compound has lower energy and more stable structure in comparison with the stabile elementary substance.

Key words: Ethylene diamine dihydrochloride; Crystal structure; Low-temperature heat capacity; Standard molar enthalpy of dissolution; Standard molar enthalpy of formation