| English | Latent heat |
|---|---|
| Bahasa Melayu | Haba pendam |
| 中文 | 潜热 |
Definition
The heat absorbed or released when a substance changes state without any change in temperature.
In exam terms
Latent heat is the heat energy absorbed or released when a substance changes state, for example melting, boiling, freezing or condensing, at constant temperature. It is a form of energy measured in joules (J).
During the change of state the energy is used to break or form the bonds between particles, not to increase their kinetic energy, so a graph of temperature against time shows a flat (horizontal) portion.
The quantity of latent heat is given by Q = mL, where Q is the heat in joules (J), m is the mass in kilograms (kg) and L is the specific latent heat in J kg⁻¹. Example of correct use: the latent heat of fusion supplied to ice melts it at 0 °C without raising its temperature.
Do not confuse it with…
Do not confuse latent heat with sensible heat (heat that causes a temperature change, Q = mcθ). Latent heat changes the state of a substance with no change in temperature, while sensible heat changes the temperature with no change of state.
During melting or boiling the thermometer reading stays constant even though heat is still being supplied.
In Paper 2 this is usually asked as state what is meant by latent heat, or explain why the temperature stays constant during melting. Always link the constant temperature to the heat being used to break the bonds between particles rather than to raise their kinetic energy.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)