Latent Heat
Definition
The hidden heat absorbed or released during a phase change — it breaks or forms molecular bonds instead of changing temperature.
Symbol: · Unit: J/kg
Technical definition
Heat per unit mass for a phase transition: Q = mL, where L is the specific latent heat (J/kg). Latent heat of fusion (melting) and vaporization (boiling); water's latent heat of vaporization (2260 kJ/kg) is exceptionally large.
Example
Boiling away 1 kg of water takes 2260 kJ — about five times the energy needed to heat it from 0°C to 100°C. That is why steam burns are so severe.
Common confusion
‘Latent’ means hidden — the heat does not show up on a thermometer. It is stored as potential energy in rearranged molecular bonds, released again when the reverse phase change happens.