How do phase diagrams work?
A phase is just another term for solid, liquid or gas. And a phase diagram is graphical representation that lets you work out exactly what phases are present at a given temperature. Every point in the diagram represents a possible combination of temperature and pressure for a closed system. The diagram is divided into three areas, which represent the solid, liquid, and gaseous states of a substance.
Phase diagrams can be used in different ways. The regions separated by the lines give us an idea of the conditions of T and P that are most likely to produce a gas, a liquid, or a solid. The lines that divide the diagram represent the combinations of T and P at which two states are in equilibrium.
To find out which area corresponds to each of the three states, remember the conditions of P and T that are most likely to be associated with a solid, a liquid or a gas. High temperatures and low pressures favor the formation of gases. And low temperatures and high pressures favor the formation of solids.
To check if you have correctly drawn a phase diagram, imagine a line from left to right at the top of the diagram which means an increase in the temperature of the system at constant pressure. When a solid is heated at constant pressure, it turns into a liquid and eventually turns into a gas.