Heat absorbed or released during a phase transition (melting, vaporization) at constant temperature.
Symbols
Q
heat of transition
[J]
m
mass
[kg]
L
latent heat of phase transition
[J/kg]
Where it comes from
During melting or vaporization the temperature does not rise — all the heat goes into changing the state of matter. That is why boiling water stays at a constant 100°C until it has all boiled away.
When to use it
Melting, vaporization, freezing, condensation (heat balance with a phase transition).
Example
Melting 0.5 kg of ice (L=334000 J/kg). Calculate the required heat.