The latent heat of fusion is the amount of heat energy required to change a substance from a solid to a liquid state without changing its temperature. It is a phase transition process, and during fusion, molecules in a solid absorb energy to break their bonds and transition into a liquid state.
Them mathematical form of latent heat of fusion is given as:
Q=m⋅Lf
Where:
- Q is the heat energy absorbed during the phase transition (in joules),
- m is the mass of the substance undergoing fusion (in kilograms),
- Lf is the latent heat of fusion for that substance (in joules per kilogram).
Daily Life Examples
Ice Melting:
- Explanation: When ice (solid water) is exposed to heat, it absorbs energy to break the bonds between water molecules, turning it into liquid water.
- Mathematical Representation: If you have, for example, 1 kg of ice (m=1 kg) and the latent heat of fusion for water is 334,000 J/kg, the amount of heat energy needed to melt the ice would be Q=1 kg×334,000 J/kg=334,000 J
Candle Wax Melting:
Explanation: When a solid candle is exposed to heat, the wax absorbs energy to break the bonds between its molecules, resulting in the transition from a solid to a liquid state.
- Mathematical Representation: Suppose you have 0.5 kg of candle wax (m=0.5 kg) with a latent heat of fusion for the wax of 200,000 J/kg. The heat energy required to melt the candle wax would be Q=0.5 kg×200,000 J/kg=100,000 J
Fusion of Solid Butter:
- Explanation: Solid butter undergoes fusion when exposed to heat, transforming from a solid to a liquid state as the molecules absorb energy to break their bonds.
- Mathematical Representation: Let’s say you have 0.8 kg of solid butter (m=0.8 kg) and the latent heat of fusion for butter is 250,000 J/kg. The heat energy required for the fusion of the butter would be Q=0.8 kg×250,000 J/kg=200,000 J.
Crux Points
- Specific to Substances:
- The latent heat of fusion is specific to each substance. Different substances require different amounts of energy to undergo fusion.
- Temperature Remains Constant:
- During the phase transition from solid to liquid, the temperature remains constant even though heat is being absorbed. This is a characteristic feature of latent heat.
- Reverse Process – Freezing:
- The same amount of heat is released when a substance undergoes the reverse process, i.e., freezing. The latent heat of fusion is also released during the transition from liquid to solid.
