Calculate the exact energy required to melt, boil, or sublimate a substance using the thermodynamic formula Q = m × L
See how energy breaks intermolecular bonds without changing temperature
Select your phase change, substance, and mass to find the latent heat energy.
Q = Total heat energy required (Joules or kJ)
m = Mass of the substance (kg)
L = Specific latent heat of the substance (kJ/kg)
Latent heat is the "hidden" energy needed to change a substance's phase without changing its temperature.
Fusion (L_f): Energy to melt a solid into a liquid.
Vaporization (L_v): Energy to boil a liquid into a gas.
Sublimation (L_s): Energy to turn a solid directly into a gas. By Hess's Law, L_s ≈ L_f + L_v.
During a phase change, all the added energy (latent heat) goes into breaking the intermolecular bonds holding the molecules together, rather than increasing their kinetic energy. Since temperature is a measure of average kinetic energy, it remains constant until the phase change is complete.
Melting (fusion) only requires enough energy to loosen the bonds so molecules can slide past each other. Vaporization requires enough energy to completely break all intermolecular bonds and separate the molecules by large distances. This requires vastly more energy.
Yes! When a gas condenses or a liquid freezes, it releases the exact same amount of latent heat that it absorbed to vaporize or melt. This is why steam burns are so severe—the steam releases its massive latent heat of vaporization directly onto your skin as it condenses.