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Citation: Zihao Xu, Jia Yao, Xiaogang Peng. Statistical thermodynamics of heat capacity of liquid and gas[J]. University Chemistry, ;2026, 41(6): 92-99. doi: 10.12461/PKU.DXHX202511181 shu

Statistical thermodynamics of heat capacity of liquid and gas

Department of Chemistry, Zhejiang University, Hangzhou 310058, Zhejiang Province, China

Corresponding author: Jia Yao, Xiaogang Peng,
Received Date: 25 November 2025
Revised Date: 29 December 2025

The molar heat capacity of ideal gas can be quantitatively calculated using quantum statistical thermodynamics. However, due to difficulty on determining degrees of freedom in liquid state, there is currently no method for directly computing the molar heat capacity of liquids. We noticed that the phase transition from gas to liquid has a limited effect on intramolecular vibrations, but converting the free translational and rotational degrees of freedom of gas molecules into quasi-vibrational degrees of freedom with very low frequency. Therefore, the molar heat capacity of a liquid can be quantitatively correlated with the molar heat capacity of the corresponding gas, calculated on the basis of evolution of quantum degrees of freedom.
- Liquid,
- Transformation of motion,
- Heat capacity,
- Quantum statistical thermodynamics
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