Specific Latent Heat

This lesson covers specific latent heat as required by the Edexcel GCSE Physics specification (1PH0), Topic 3: Conservation of Energy. You need to understand what latent heat is, distinguish between latent heat of fusion and vaporisation, use the equation, and interpret heating curves.

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What Is Latent Heat?

When a substance changes state (e.g., solid to liquid, or liquid to gas), energy is needed — but the temperature does not change during the change of state.

Latent heat is the energy required to change the state of a substance without changing its temperature.

The word "latent" comes from Latin and means hidden — the energy is "hidden" because it does not cause a temperature rise.

Why Does the Temperature Stay Constant?

During a change of state:

• The energy supplied is used to break (or form) intermolecular bonds between particles.
• The energy goes into overcoming the attractive forces between particles, not into increasing their kinetic energy.
• Since temperature is a measure of the average kinetic energy of particles, and the kinetic energy does not change, the temperature remains constant.