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.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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