Innovative insights into which statements the third law of thermodynamics includes exactly

Xiaohang Chen, Yinghui Zhou, Jincan Chen

Published 2023-08-30Version 1

It is found from textbooks and literature that the third law of thermodynamics has three different statements, i.e., the Nernst theorem, unattainability statement of absolute zero temperature, and heat capacity statement. It is pointed out that such three statements correspond to three thermodynamic parameters, which are, respectively, the entropy, temperature, and heat capacity, and can be obtained by extrapolating the experimental results of different parameters at ultra-low temperatures to absolute zero. It is expounded that because there's no need for additional assumptions in the derivation of the Nernst equation, the Nernst theorem should be renamed as the Nernst statement. Moreover, it is proved that both the Nernst statement and the heat capacity statement are mutually deducible and equivalent, while the unattainability of absolute zero temperature is only a corollary of the Nernst statement or the heat capacity statement so that it is unsuitably referred to as one statement of the third law of thermodynamics. The conclusion is that the Nernst statement and the heat capacity statement are two equivalent statements of the third law of thermodynamics.