GCSE Physics · Edexcel 1PH0 · Topic 14B
Changes of state and specific latent heat
Key points
- Changes of state: melting, freezing, boiling (evaporating), condensing and sublimating. They are physical changes and mass is conserved.
- During a change of state, energy is used to break (or released when forming) bonds between particles, so the temperature stays constant.
- Specific latent heat () is the energy needed to change the state of 1 kg without a temperature change: , with in J/kg.
- Latent heat of fusion is for melting/freezing; latent heat of vaporisation is for boiling/condensing (usually much larger).
- A heating curve has flat sections at the melting and boiling points.
- Heating a substance increases its internal energy (the total kinetic and potential energy of its particles).
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When a substance melts or boils, energy goes in but the temperature does not rise. Specific latent heat measures how much energy these changes of state need, and the particle model explains where that energy goes.
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