# Latent heat

Energy absorbed or released when a substance changes state without changing temperature. Q = m L.

Physics (university) · Part 06: Thermodynamics · Card 4 of 10 · Last updated 2026-10-19

## Analogy

Melting ice in a drink cools it without warming the ice.

## Example

**Melting ice**

L fusion = 334,000 J/kg
Q = 1 x 334,000
Q = 334 kJ

## In practice

Melting 1 kg of ice at 0 degrees Celsius takes about 334,000 J.

## Practice

### Flashcards

- **What is latent heat?** Energy for a change of state at constant temperature.

## Questions people ask

### Why does boiling water stay at 100 degrees Celsius?

During boiling, extra heat goes into breaking bonds between molecules, not into raising the speed of molecules. This energy is the latent heat of vaporisation, about 2.26 million J per kg for water. Only after all the water has turned to steam does the temperature rise again.

### Why does steam burn more than boiling water?

Steam at 100 degrees Celsius gives out its latent heat as it condenses on your skin. That is about 2.26 million J per kg, more than five times the energy needed to heat the same water from 0 to 100. The extra energy is why steam burns are severe.

## Related concepts

- [Temperature](https://studyvisually.com/learn/science/physics-university/physics-university-part-6/physics-university-part-6-concept-1)
- [Thermal expansion](https://studyvisually.com/learn/science/physics-university/physics-university-part-6/physics-university-part-6-concept-2)
- [Specific heat](https://studyvisually.com/learn/science/physics-university/physics-university-part-6/physics-university-part-6-concept-3)
- [Heat transfer](https://studyvisually.com/learn/science/physics-university/physics-university-part-6/physics-university-part-6-concept-5)

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