Classical ideal curves in the phase diagram for simple substances

In this paper, the curves of an ideal gas, ideal enthalpy, and ideal internal energy, united by a common definition of classical ideal curves (CICs), are considered. It is shown that the configurational parts of the thermodynamic properties, such as enthalpy $H$, internal energy $U$, $PV$, and temperature $T$, change linearly in these curves. The explanation of the behavior of CICs is proposed by representing the properties as the sum of internal and thermal components. A model of interrelated termination temperatures and densities of these ideal curves is developed. An expression for the "potentiale of mean force" is obtained, reflecting the linearity of the thermodynamic properties in the classical ideal curves.