Thermodynamic investigation of room temperature ionic liquid |
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Authors: | Z. H. Zhang L. X. Sun Z. C. Tan F. Xu X. C. Lv J. L. Zeng Y. Sawada |
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Affiliation: | (1) Materials and Thermochemistry Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, P.R. China;(2) Graduate School of the Chinese Academy of Sciences, Beijing, P.R. China;(3) Department of Nanochemistry, Faculty of Engineering, Tokyo Polytechnic University, 1583 Iiyama, Atsugi, Kanagawa 243-0297, Japan |
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Abstract: | 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, C p,m [J K−1 mol−1]=181.43+51.297X −4.7816X 2−1.9734X 3+8.1048X 4+11.108X 5 [X=(T−135)/55] for the solid phase (80–190 K), C p,m [J K−1 mol−1]= 349.96+25.106X+9.1320X 2+19.368X 3+2.23X 4−8.8201X 5 [X=(T−225)/27] for the glass state (198–252 K), and C p,m[J K−1 mol−1]= 402.40+21.982X−3.0304X 2+3.6514X 3+3.4585X 4 [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 ΔH g=2.157 kJ mol−1 and ΔS g=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 ΔH m = 8.453 kJ mol−1 and ΔS m=30.21 J K−1 mol−1. Using oxygen-bomb combustion calorimeter, the molar enthalpy of combustion of BPBF4 was determined to be Δc H m0 = −5451±3 kJ mol−1. The standard molar enthalpy of formation of BPBF4 was evaluated to be Δf H m0 = −1356.3±0.8 kJ mol−1 at T=298.150±0.001 K. |
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Keywords: | BPBF4 combustion calorimetry glass transition heat capacity room temperature ionic liquid phase transition standard enthalpy of formation |
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