The molar heat capacities of the room temperature ionic liquid 1-butylpyridinium tetrafluoroborate (BPBF4) were measured 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]=181.43+51.297X −4.7816X2−1.9734X3+8.1048X4+11.108X5 [X=(T−135)/55] for the solid phase (80–190 K), Cp,m [J K−1 mol−1]= 349.96+25.106X+9.1320X2+19.368X3+2.23X4−8.8201X5 [X=(T−225)/27] for the glass state (198–252 K), and Cp,m[J K−1 mol−1]= 402.40+21.982X−3.0304X2+3.6514X3+3.4585X4 [X=(T−338)/52] for the liquid phase (286–390 K), respectively. According to the polynomial equations and thermodynamic relationship,
the values of thermodynamic function of the BPBF4 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 BPBF4 was observed at 194.09 K, the enthalpy and entropy of the glass transition were determined to be ΔHg=2.157 kJ mol−1 and ΔSg=11.12 J K−1 mol−1, respectively. The result showed that the melting point of the BPBF4 is 279.79 K, the enthalpy and entropy of phase transition were calculated to be ΔHm = 8.453 kJ mol−1 and ΔSm=30.21 J K−1 mol−1. Using oxygen-bomb combustion calorimeter, the molar enthalpy of combustion of BPBF4 was determined to be ΔcHm0 = −5451±3 kJ mol−1. The standard molar enthalpy of formation of BPBF4 was evaluated to be ΔfHm0 = −1356.3±0.8 kJ mol−1 at T=298.150±0.001 K.