Ideality contours and thermodynamic regularities in supercritical molecular fluids

Highlights: • Expanded Wang-Landau simulations yield the ideality contours of SF₆, CO₂ and H₂O. • Boyle and H parameters increase with the strength of intermolecular interactions. • Shape of ideality contours retained for the 3 fluids. • First step towards a correspondence between the supercritical fluids of different compounds. Using Expanded Wang-Landau simulations, we calculate the ideality contours for 3 molecular fluids (SF₆, CO₂ and H₂O). We analyze how the increase in polarity, and thus, in the strength of the intermolecular interactions, impacts the contours and thermodynamic regularities. This effect results in the increase in the Boyle and H parameters, that underlie the Zeno line and the curve of ideal enthalpy. Furthermore, a detailed analysis reveals that dipole–dipole interactions lead to much larger enthalpic contributions to the Gibbs free energy. This accounts for the much higher temperatures and pressures that are necessary for supercritical H₂O to achieve ideal-like thermodynamic properties.