A level Physics · Edexcel 9PH0 · Topic 9A
Specific heat capacity and latent heat
Key points
- Specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1 K: (J kg K).
- Specific latent heat is the energy needed to change the state of 1 kg without changing temperature: . Use fusion for melting and vaporisation for boiling.
- During a change of state the temperature stays constant: energy breaks bonds, raising potential energy, not kinetic energy.
- Internal energy = sum of the randomly distributed kinetic and potential energies of the molecules.
- With an electrical heater, energy supplied = .
- Core practical: find the specific latent heat of a phase change (e.g. melting ice with an immersion heater). A similar method finds from the gradient of temperature against time. Insulate to reduce heat loss.
- Heat losses mean the calculated is usually larger than the true value.
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Supplying energy to a substance can raise its temperature or change its state. Specific heat capacity and specific latent heat tell you how much energy each of these needs per kilogram.
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