Latent Heat
Latent heat is the energy absorbed or released during a change of state at constant temperature, given by Q = mL.
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Meaning of latent heat
Latent heat is the energy required to change the state of unit mass of a substance without changing its temperature. For melting/freezing, we use latent heat of fusion; for boiling/condensation, latent heat of vaporisation. The total energy absorbed or released is Q = mL.
Bond breaking and forming
During melting or boiling, energy is used mainly to overcome intermolecular forces and increase the separation between particles, not to increase their kinetic energy. That is why temperature remains constant even though energy is supplied. The reverse happens during freezing or condensation.
Why does ice at 0°C require more energy to become water at 0°C, even though the temperature is the same?