Which two phrases require the removal of heat energy

The two phases that require the removal of heat are when a liquid turns to solid (e.g. freezing)  and when a gas turns to liquid (e.g. condensation)

Heat will leave the liquid as it freezes, and heat will leave the gas as it condenses into liquid.

The change in phase of a substance will always involve a change of heat. Heat, which is energy, either comes into the material during the phase change or heat comes out of the material during this change.

However, although the heat content of the material changes, the temperature does not, it remains the same during the phase change.

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