Editing Phase diagram (section)

== Overview ==
Common components of a phase diagram are ''lines of equilibrium'' or ''phase boundaries'', which refer to lines that mark conditions under which multiple phases can coexist at equilibrium.  Phase transitions occur along lines of equilibrium. [[Metastable]] phases are not shown in phase diagrams as, despite their common occurrence, they are not equilibrium phases.

[[Triple point]]s are points on phase diagrams where lines of equilibrium intersect.  Triple points mark conditions at which three different phases can coexist.  For example, the water phase diagram has a triple point corresponding to the single temperature and pressure at which solid, liquid, and gaseous water can coexist in a stable equilibrium ({{val|273.16|ul=K}} and a partial vapor pressure of {{val|611.657|ul=Pa}}). The pressure on a pressure-temperature diagram (such as the water phase diagram shown) is the [[partial pressure]] of the substance in question.<ref>{{Cite web |url=http://ch302.cm.utexas.edu/physEQ/physical/selector.php?name=phase-diag |title=Phase Diagrams |access-date=2023-07-14 |website=ch302.cm.utexas.edu}}</ref> 

The [[solidus (chemistry)|solidus]] is the temperature below which the substance is stable in the solid state. The [[liquidus]] is the temperature above which the substance is stable in a liquid state. There may be a gap between the solidus and liquidus; within the gap, the substance consists of a mixture of crystals and liquid (like a "[[slurry]]").<ref>{{cite book |last1=Predel |first1=Bruno |last2=Hoch |first2=Michael J. R. |last3=Pool |first3=Monte |year=2004 |title=Phase Diagrams and Heterogeneous Equilibria: A Practical Introduction |publisher=[[Springer (publisher)|Springer]] |isbn=978-3-540-14011-5}}<!-- Reference 1 covers most of the article.--></ref>

[[Working fluids]] are often categorized on the basis of the shape of their phase diagram.