Calculates the heat energy absorbed or released during a phase change, like ice melting or water boiling, at constant temperature.
How it works
Mass is multiplied directly by the substance’s latent heat value for the specific phase change.
What this does not include
This does not include heat needed for a temperature change within a single phase — for that, use this site’s specific heat calculator instead, which handles temperature change rather than phase change.
How to use this calculator
- Enter the mass and select the phase change (fusion or vaporization of water).
A worked example
2 kg of ice melting, latent heat of fusion 334,000 J/kg: heat required = mass × latent heat = 2 × 334,000 = 668,000 J.
0.5 kg of water vaporizing, latent heat of vaporization 2,260,000 J/kg: heat required = 1,130,000 J — vaporization takes far more energy per kilogram than melting.
What the variables mean
| Variable | Meaning |
|---|---|
| Mass | Mass undergoing the phase change |
| Latent heat | Energy required per kilogram for that specific phase change |
Edge cases worth knowing
Latent heat is absorbed or released without a temperature change. Melting ice at 0°C stays at 0°C the entire time it’s melting — the energy goes into breaking molecular bonds, not raising temperature.
A negative mass has no physical meaning, so the calculator declines to show a result for one.
Frequently asked questions
Why does temperature stay constant during a phase change?
All the added (or removed) energy goes into breaking (or forming) molecular bonds during the phase transition, rather than increasing the substance’s kinetic energy (temperature) directly.
Why is vaporization’s latent heat so much higher than fusion’s?
Turning liquid water into vapor requires completely separating molecules from each other, while melting ice only needs to loosen the rigid crystal structure — separating molecules entirely takes much more energy.
Does this apply to freezing and condensing too?
Yes — the same magnitude of energy is released during freezing or condensing as is absorbed during melting or vaporizing; only the direction of energy flow reverses.
