Thermodynamic and Transport Properties of Supercritical Fluids: Review of Thermodynamic Properties (Part 1)

This review presents the results of a detailed analysis of the role of isochoric heat capacity as a key thermodynamic property of matter in the investigation of critical and supercritical phenomena. A brief historical background is given on the role and contribution of Russian scientific schools to the experimental investigation of the isochoric heat capacity in the critical region in the development of the nonclassical (scaling) theory of critical phenomena, which drastically changed the understanding of the physical nature of critical and supercritical phenomena. The experimental behavior of the isochoric heat capacity and other thermodynamic properties of fluids in the critical and supercritical regions related to it is investigated in detail. The role of new experimental studies of two-phase isochoric heat capacity near the critical point in the development of a “complete” scaling theory is discussed. This theory allows us to understand the physical nature of the asymmetry of the liquid–gas coexistence curve near the critical point and to estimate the contribution of the chemical potential to the divergence of the two-phase isochoric heat capacity at the critical point. The review also focuses on supercritical phase transitions and the role of isochoric heat capacity in determining the Widom line, which separates the liquid-like and gas-like regions in supercritical states; i.e., it defines the boundaries of the coexistence of liquid-like and gas-like phases in supercritical fluids.