Solid to liquid transitions (and vice versa) can be caused by heating and cooling. Liquid to gas transitions (and vice versa) can be caused by heating,cooling and change of pressure.
Work Step by Step
Solids can be converted to liquids by heating, and liquids can be cooled to form solids. In the case of gas and liquid, heating and cooling can change states from liquid to gas and gas to liquid. But this transition can also be done by changing pressure. Gas can liquefy under high pressure and liquid can turn to gas under low pressure. For example, propane is liquefied at high pressures and stored in cylinders. When the cylinder opens, or when the pressure is reduced, it re forms into its gaseous state.