Study on the thermodynamic properties for ionic liquid [C6mim][OAc](1-hexyl-3-methylimidazolium acetate)

•ΔsolHmθ for [C6mim][OAc] were obtained in the temperature range of (288.15 to 308.15 ± 0.01) K.•The ΔCp,mθ,   ΔCpθ, (ΔH+ + ΔH−), ΔH+ ([C6mim]+) for [C6mim][OAc] solution were calculated.•The apparent relative molar heat capacity, ΦCp, were also calculated for [C6mim][OAc].

Using the solution-reaction isoperibol calorimeter, molar enthalpies of solution in water, ΔsolHm, for ionic liquid [C6mim][OAc] with different molalities were measured in the temperature range from (288.15 to 308.15 ± 0.01) K with an interval of 5 K. According to Archer's method, the values of the standard molar enthalpies of solution, ΔsolHmθ, were obtained for [C6mim][OAc], respectively. According to Glasser's theory of lattice energy, the hydration enthalpy of cation and anion in infinite dilution aqueous [C6mim][OAc] was calculated, (ΔH+ + ΔH−) = −598 kJ mol−1, at 298.15 K. The hydration enthalpy of the cation, ΔH+ ([C6mim]+) = −173 kJ mol−1, was determined. In comparison with hydration enthalpy of [C2mim]+, the hydration enthalpy of [C6mim]+ is a little bit weaker. A linear relationship was found by plotting the experimental values of ΔsolHmθ against (T  —298.15) K. The standard molar heat capacity of solution, ΔCp,mθ = 313 J K−1 mol−1, was obtained from the slope of the regression line, the specific heat capacity of solution, ΔCpθ = 1.38 J g−1 K−1, and the apparent relative molar heat capacity, ΦCp, were also calculated for [C6mim][OAc].