Substances can change their state—such as from solid to liquid or from liquid to gas—by absorbing or releasing heat. These transitions occur at specific temperatures and are categorized as follows:
- Melting: Solid to liquid
- Freezing: Liquid to solid
- Vaporization: Liquid to gas
- Condensation: Gas to liquid
- Sublimation: Solid to gas
- Deposition: Gas to solid
These changes happen at fixed temperatures under constant pressure, known as the melting point, boiling point, etc.
Latent Heat
When a substance undergoes a change of state, its temperature does not change during the process. The heat energy supplied or removed at this stage is known as latent heat. This energy is used to overcome or establish intermolecular forces rather than changing temperature.
There are two key types of latent heat:
- Latent Heat of Fusion (Lf): The heat required to convert 1 kg of a substance from solid to liquid at its melting point, without a temperature change.
- Latent Heat of Vaporization (Lv): The heat required to convert 1 kg of a substance from liquid to gas at its boiling point, without a temperature change.
The energy involved in a phase change can be calculated using the formula:
\(Q = mL\)
Where:
- Q = heat absorbed or released (in joules)
- m = mass of the substance (in kg)
- L = specific latent heat (J/kg)
Since temperature remains constant during a change of state, latent heat is crucial for understanding the energy required for physical transformations in matter.
Written by Thenura Dilruk