Phase diagram
![A typical phase diagram. The solid green line applies to most substances; the dotted green line gives the anomalous behavior of water. The green lines mark the freezing point and the blue line the boiling point, showing how they vary with pressure.](/Images/godic/202502/02/Phase-diag2.svg3530.png")
![Temperature vs. specific entropy phase diagram for water/steam. In the area under the red dome, liquid water and steam coexist in equilibrium. The critical point is at the top of the dome. Liquid water is to the left of the dome. Steam is to the right of the dome. The blue lines/curves are isobars showing constant pressure. The green lines/curves are isochors showing constant specific volume. The red curves show constant quality.](/Images/godic/202502/02/TS-Wasserdampf_engl3530.png")
![](/Images/godic/202502/02/Mollier_enthalpy_entropy_chart_for_steam_-_US_units.svg3530.png")
![](/Images/godic/202502/02/Pressure-enthalpy_chart_for_steam,_in_US_units.svg3530.png")
- For the use of this term in mathematics and physics, see phase space.
A phase diagram in physical chemistry, engineering, mineralogy, and materials science is a type of chart used to show conditions (pressure, temperature, volume, etc.) at which thermodynamically distinct phases occur and coexist at equilibrium.