Physics Form 4: Chapter 4 - Latent Heat

Latent heat is the quantity of heat absorbed or released by a substance to change its physical state without any change in temperature.

 

• Specific latent heat of fusion is the quantity of heat needed to change 1kg of a solid to liquid at its melting point without change in temperature.
• The temperature does not change even though heat is being absorbed by the solid particles. This is because the heat absorbed does not increase the kinetic energy of particles but is used to overcome the force of attraction between the particles.

• Specific latent heat of vaporization is the quantity of heat needed to change 1kg of a liquid to gas at its boiling point without change in temperature.
• The temperature does not change even though heat is being absorbed by the liquid particles. This is because the heat absorbed does not increase the kinetic energy of particles but is used to overcome the force of attraction between the particles.

 

Specific latent heat of vaporization is greater than its specific latent heat of fusion because:

• More energy is required to break the bonds between liquid molecules in order to change into gas phase.
• Extra energy is required to overcome atmospheric pressure.
• Energy is used to overcome the surface tension of a liquid when its molecules change into the gas phase.

   
Further information about latent heat