The Fermi–Dirac Distribution as a Model of a Thermodynamically Ideal Liquid. Phase Transition of the First Kind for Neutral Gases (Corresponding to NonpolarMolecules)

In this paper, we introduce the notion of a thermodynamically ideal liquid and calculate the temperature below which it appears. This temperature is $T=0.84 T_c$, where $T_c$ is the critical temperature of a gas whose molecules are nonpolar. For such a gas, in a sufficiently wide neighborhood of the binodal, the isotherms of a gas and of a thermodynamically ideal liquid coincide with those of a van der Waals gas for the critical value of the compressibility factor $Z_c=3/8$. In this sense, for $T\leq 0.84 T_c$ and the particular case $Z_c=3/8$, the developed theory is a generalization of the van der Waals model. A new phase transition of the second kind at the point of zero activity is described.