Latent heat is the heat required to change a material without a change in temperature. An example of this is while boiling water. After the boiling temperature is met, a large quantity of heat is expended to change the liquid water into steam vapor. The heat that is added while the temperature stays constant is called latent heat.
It used to be thought that heat was an actual substance and the heat expended to change phases was hidden or latent. Thermodynamics has shown that heat is not a substance but a form of energy and the latent heat in turning water into steam is used to break the molecular bond between the water molecules.
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