English: PT diagram. In this cause we are looking pressure vs temperature. This diagram is often referred to as the phase diagram. In this diagram you will be able to see three different lines. This line represent sublimation, melting, and vaporization. Where these lines intersect is called the triple point. The triple point is where all three phases coexist in equilibrium.

PV diagram. In this cause we are looking at pressure, P, vs the molar volume, V_m, of a pure substance. In turn, this property diagram is very similar to the T-V diagram except instead of there being a constant pressure the temperature is constant. Like the T-V diagram there is a critical point. The critical point represents where the critical pressure, critical specific volume, critical temperature intersect.

A TV diagram is a property diagram that relates temperature to molarc volume when a pure substance is at a constant pressure. On the phase change line, or saturation line, the pure substance will exist as a liquid and a gas. In addition, as energy is added into the system the molar volume of the substance will increase while the temperature remains the same. Finally, the lower pressure is in comparison to the critical pressure, the longer this phase change line will be.