Abstract: A colorless and transparent ionic liquid BMIC/ZnCl₂ was prepared by mixing 1-butyl 3-methylimidazolium chloride(BMIC) and ZnCl₂ with a molar ratio of 1:1 at 363.15 K under stirring in a glove box filled with dry argon. The molar dissolution enthalpies, Δ_sH_m, of BMIC/ZnCl₂ in water with various molalities were determined by a solution-reaction isoperibol calorimeter at 298.15 K. In terms of Pitzer electrolyte solution theory, the molar solution enthalpy of BMIC/ZnCl₂ at infinite dilution, Δ_sH⁰_m, and Pitzer parameters: β^(0)L_MX, β^(1)L_MX and C^φL_MX were obtained, respectively. According to Lecocq's viewpoint, ionic liquid BMIC/ZnCl₂ with a molar ratio of 1:1 is a single compound BMIZnCl₃. In terms of Glasser's theory and thermodynamic cycle, the standard molar hydration enthalpy of ionic liquid BMIZnCl₃, (ΔH⁰₊ +ΔH⁰_-)=-497 kJ/mol, was calculated. The standard molar enthalpies of hydration of individual ions can be obtained from those of electrolytes, provided that the value of one ion is known. The standard molar enthalpies of hydration of cation BMI⁺ were estimated ΔH⁰₊(BMI⁺)=-225 kJ/mol in literature so that the standard molar enthalpies of hydration of ZnCl^-₃ was obtained, that is, ΔH⁰_-(ZnCl^-₃) =-272 kJ/mol.

Key words: Isoperibol calorimeter, Solution enthalpy, Pitzer’s equationy, Ionic liquid, Hydration enthalpy