Figure 3.6: P-v Diagram And Phase Envelope Of A Pure Substance
If you carefully follow the trend of the critical isotherm (@ T = Tc in Fig. 3.5), you will realize that it has a point of inflexion (change of curvature) at the critical point. Furthermore, the critical point also represents the maximum point (apex) of the P-v envelope. Mathematically, this information is conveyed by the expressions