Molar heat capacity and thermodynamic properties of N-alklypyridinium hexafluorophosphate salts, [Cnpy][PF6] (n = 2, 3, 5)

•Targets of this research are hydrophobic series ionic liquids.•Molar heat capacities (Cp,m) were determined.•Influences of methylene on molar heat capacity were discussed.•Thermodynamic functions (HT − H298.15) and (ST − S298.15) were determined.

Molar heat capacities (Cp,m) of the ionic liquids (ILs) N-alkylpyridinium hexafluorophosphate [Cnpy][PF6] (n = 2, 3, 5) were measured with a high-precision automated adiabatic calorimeter (AC). The melting temperatures were determined. The molar enthalpy and entropy of phase transition were calculated according to the data obtained of the molar heat capacities by the empirical equation. The polynomial equations of molar heat capacity as a function of the temperature were fitted before and after the phase transition for each IL compounds. The thermodynamic functions (HT − H298.15) and (ST − S298.15) were derived from the molar heat capacity values over the temperature range from (80 to 400) K with an interval of 5 K.