Comments On the heat capacity of liquids at high temperatures, S.M. Stishov, Physica A 478 (2017) 205

TL;DR

This paper investigates how the isochoric heat capacity of liquids and dense gases decreases with temperature, linking this behavior to particle interactions, and introduces models and criteria to describe this phenomenon.

Contribution

It provides new explicit expressions for the Frenkel line and demonstrates the applicability of the Carnahan-Starling equation to describe heat capacity in liquids.

Findings

Isochoric heat capacity decreases with temperature across various potentials.

Radial distribution functions can describe temperature dependence of heat capacity.

Carnahan-Starling equation accurately models argon's heat capacity.

Abstract

It is shown that the isochoric heat capacity of dense gas, fluid and liquid decreases with increasing temperature at arbitrary values of a density for many pair interaction potentials, including bonded potentials; that a decrease of the isochoric heat capacity of the liquid with increasing temperature is related to a decrease of the interaction between the particles with increasing temperature; that a radial distribution function for nonideal dilute gas, which is independent of density, can describe a temperature dependence of the isochoric heat capacity of liquid argon; that a radial distribution function dependent on the density and temperature describes a temperature dependence of the isochoric heat capacity of liquid and dense fluid; that the Carnahan-Starling equation of state for soft spheres gives a good quantitative description of the isochoric heat capacity of argon; that the fluctuations of the kinetic energy increases with temperature faster than that of the potential energy; and finally, that a liquid state can be considered as a state of dense gas. The explicit expressions to define the Frenkel line on the (temperature, density) plane are derived.