Determination of the Molar Enthalpy of Solution for Ionic Liquid [C5mim][OAc](1-pentyl-3-methylimidazolium acetate) in the Temperature Range from 288.15 to 308.15 K

Abstract

The molar enthalpies of solution, ΔsolHm, for ionic liquid [C5mim][OAc] with different molalities were measured by the solution-reaction isoperibol calorimeter in the temperature range from 288.15 to 308.15 K with an interval of 5 K. According to Archer’s method, the standard molar enthalpies of solution, ΔsolHmθ, and the apparent relative molar enthalpy, ΦL, for [C5mim][OAc] were determined. In terms of Glasser’s theory of lattice energy, the hydration enthalpy of the cation, ΔH+ ([C5mim]+) = −178 kJ·mol–1 was obtained at 298.15 K. Compared with hydration enthalpy of [C2mim]+, ΔH+ ([C2mim]+) = −233 kJ·mol–1, the hydration of [C5mim]+ is weaker than [C2mim]+. The plot of ΔsolHmθ vs (T – 298.15) K is a good straight line and its slope is the standard molar heat capacity of solution, ΔCp,mθ = 231 J·K–1·mol–1, so that the specific heat capacity of solution, ΔCpθ = 1.09 J·g–1·K–1, was obtained for IL [C5mim][OAc].