Latent heat is the energy needed to change the state of a substance — solid to liquid, or liquid to gas — at constant temperature. While ice melts at 0 °C, all the heat goes into breaking bonds, not raising the temperature.
This calculator multiplies the mass by the specific latent heat: Q = mL. The same amount of heat is given out when the substance changes back (freezing or condensing).
| Change of state (latent heat, J/kg) | Melting ice / freezing water (334,000) |
| Mass (m) | 2 kg |
| Heat energy Q (J) | 668,000 |
| Heat energy (kJ) | 668 |
| Heat energy (kcal) | 159.656 |
Melting 2 kg of ice at 0 °C takes 668 kJ.
Try this example →| Change of state (latent heat, J/kg) | Boiling water / condensing steam (2,260,000) |
| Mass (m) | 0.5 kg |
| Heat energy Q (J) | 1,130,000 |
| Heat energy (kJ) | 1,130 |
| Heat energy (kcal) | 270.076 |
Turning 0.5 kg of water at 100 °C into steam takes 1,130 kJ.
Try this example →Steam at 100 °C releases its latent heat of vaporisation (2,260 kJ/kg) when it condenses on skin, on top of the heat released as the water then cools. That is about 5 times more energy than water at 100 °C cooling to body temperature.
Heat absorbed or released during a change of state without any change in temperature.
About 334,000 J/kg (334 J/g, or 80 cal/g).
About 2,260,000 J/kg (2,260 J/g, or 540 cal/g).
The energy goes into breaking the bonds that hold the solid together instead of making the molecules move faster.