1. Supercritical state

Pure substances can be found in either solid, liquid or gaseous states; in the temperature-pressure diagram (figure 1 ), the regions corresponding to these three states are separated by change-of-state curves converging at the triple point. As it happens, the vaporization curve (liquid-gas) has a stopping point known as the critical point (CP), corresponding to a pressure-temperature pair (p _c , T _c ) that is fairly easy to reach for most simple organic compounds.

Beyond this critical point ( $p>p_{\text{c}}$ and $T>T_{\text{c}}$...