Heat of Vaporization/Fusion Calculator
Calculate the heat required to vaporize or melt a substance using Q = mL.
Includes common substances with known latent heat values.
Phase changes (melting and vaporization) require energy without changing temperature. This energy is called latent heat:
Q = mL
Where:
- Q = Heat absorbed or released (joules)
- m = Mass of the substance (kg)
- L = Latent heat (J/kg) — specific to each substance and phase change type
Types of latent heat:
- Heat of fusion (L_f): Energy to melt solid → liquid (or released when freezing)
- Heat of vaporization (L_v): Energy to boil liquid → gas (or released when condensing)
Latent heat reference values:
| Substance | L_fusion (kJ/kg) | L_vaporization (kJ/kg) |
|---|---|---|
| Water | 334 | 2,260 |
| Ethanol | 109 | 841 |
| Nitrogen | 25.7 | 199 |
| Iron | 247 | 6,340 |
| Lead | 24.5 | 858 |
Why L_v » L_f: Melting requires only separating molecules enough to move past each other. Vaporization requires completely breaking all intermolecular bonds and expanding the gas against atmospheric pressure — much more energy.
Why water has such a high L_v: Water molecules form strong hydrogen bonds. Boiling water requires breaking these bonds. This high latent heat is why sweating (evaporation) cools the body so effectively — each gram of sweat evaporated removes 2,260 J from your skin.