# Why is the heat energy used to overcome the intermolecular force only when it reaches melting point or boiling point?

When heat is supplied to water, for example, the temperature of water increases with the rise in heat energy but when the temperature reaches $$0^\circ$$centigrade or $$100^\circ$$centigrade, the heat energy is used to counter the intermolecular force and the temperature remains constant until all the ice has converted to water or all the water has converted to vapour. My question is that why is the heat energy not used to counter the intermolecular force when the temperature is not at melting or boiling point? Why does the vibration or the temperature keep on increasing even if the intermolecular force is not countered?

• You don't need 100 C to break molecular bonds. Liquid water evaporates to water vapor at all temperatures, and even ice evaporates. There is nothing magical about 100 C. May 5 at 11:16

If the heat energy countered the intermolecular forces, let say at $$80^\circ$$ celsius, then $$80^\circ$$ celsius would be considered as boiling point. At $$100^\circ$$ Celsius the heat energy is very strong so that it can break the intermolecular forces between the molecules.