Thermodynamics of multicomponent mixtures near the liquid-vapor critical point

A general approach based on parameterization of physical properties by two scaling functions is proposed to describe the physical properties of multicomponent mixtures in the vicinity of critical points. The present approach allows us to obtain explicit expressions for anomalous parts of various thermodynamic parameters. The temperature dependencies of pressure, of the isochoric heat capacity $C_{\rho,x}$, and of the intensity of scattered light were measured near the liquid-vapor critical point of a three-component mixture, methane$+0.35$ mol propane$+0.15$ mol pentane. $P$-$T$ measurements were carried out at $10$ isochores for densities $0.185$–$0.444$ g/cm$^3$. Measurements of $C_{\rho,x}$ and the intensity of light scattering were carried out at $4$ and $3$ near-critical isochores, respectively. Comparison of the experimental data and theoretical calculations showed that the present approach provides a quantitative description of the experimental data, and thereby, the complete equation of state of the studied system was derived.