Molal Enthalpy of Solution of Ionic Liquid [C 2 mim][GaCl 4 ]

An ionic liquid (IL), [C 2 mim][GaCl 4 ] (1‐ethyl‐3‐methylimidazolium chlorogallate), was prepared by directly mixing 1‐ethyl‐3‐methylimidazolium chloride ([C 2 mim][Cl]) and anhydrous GaCl 3 with a molar ratio of 1/1 under dry argon. The molal enthalpies of solution, Δ s H m , of [C 2 mim][GaCl 4 ], were measured over a molality range of about 0.008–0.1 mol·kg −1 by a solution reaction isoperibol calorimeter at 298.15 K. Considering the hydrolization of anion [GaCl 4 ] − in dissolution process of the IL, a new method of determining the standard molal enthalpy of solution, Δ s H m ⊖ , was put forward on the basis of Pitzer's mixed electrolyte solution theory so that Δ s H m ⊖ =−132 kJ·mol −1 and the sum of Pitzer's parameters: 4 β Ga,Cl (0) +4 β [C2mim],Cl (0) +4 Ca,[C2mim] =−0.1373076, β Ga,Cl (1)L + β   [C   2 mim],Cl(1)L =0.3484209 were obtained. In terms of thermodynamic cycle and Glasser's theory of lattice energy for IL, the dissociation enthalpy of [GaCl 4 ] − (g), Δ H dis ([GaCl 4 ] − )≈5855 kJ·mol −1 , that is enthalpy change for the reaction: [GaCl 4 ] − (g)→Ga 3+ (g)+4Cl − (g), was estimated.