Latent Heat
The energy absorbed or released when a substance changes state, with no accompanying change in temperature.
Formula / equation
q = m × L
Unit
kJ/kg
In depth
The energy goes entirely into overcoming intermolecular forces rather than increasing kinetic energy, which is why a phase change appears as a flat plateau on a heating curve. Latent heat of vaporisation is always far larger than that of fusion, since separating molecules completely costs much more than merely mobilising them.
Examples in the real world
Water needs 334 kJ/kg to melt but 2260 kJ/kg to boil, which is why steam carries so much energy.