Thermodynamic investigation of room temperature ionic liquid - The heat capacity and thermodynamic functions of BMIPF6

The molar heat capacities of the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluoroborate (BMIPF6) weremeasured by an adiabatic calorimeter in temperature range from 80 to 390 K. The dependence of the molar heat capacity on temperature is given as a function of the reduced temperature (X) by polynomial equations, CP, m (J K-1 mol(-1)) = 204.75 + 81.421X-23.828 X-2 + 12.044X(3) + 2.5442X(4) [X = (T - 132.5)/52.5] for the solid phase (80-185 K), C-P,C-m (J K-1 mol(-1)) = 368.99 + 2.4199X + 1.0027X(2) + 0.43395X(3) [X = (T -230)/35] for the glass state (195 - 265 K), and C-P,C-m (J K-1 mol(-1)) = 415.01 + 21.992X - 0.24656X(2) + 0.57770X(3) [X = (T - 337.5)/52.5] for the liquid phase (285-390 K), respectively. According to the polynomial equations and thermodynamic relationship, the values of thermodynamic function of the BMIPF6 relative to 298.15 K were calculated in temperature range from 80 to 390 K with an interval of 5 K. The glass transition of BMIPF6 was measured to be 190.41 K, the enthalpy and entropy of the glass transition were determined to be Delta H-g = 2.853 kJ mol(-1) and Delta S-g = 14.98 J K-1 mol(-1), respectively. The results showed that the milting point of the BMIPF6 is 281.83 K, the enthalpy and entropy of phase transition were calculated to be Delta(Hm) = 20.67 kJ mol(-1) and Delta(Sm) = 73.34 J K-1 mol(-1)