Latent Heat of Fusion (Solid to Liquid Change):
- The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion.
- For instance, the heat energy absorbed by ice to change the state of ice from solid to liquid, without showing any rise in temperature depicts latent heat of fusion.
- Here the heat is considered to be hidden into the contents of the beaker and is known as the latent heat.
- When a solid melts, it absorbs heat to form liquid. The reverse of that is also true.
- That is, when a liquid freezes to form a solid, an equal amount of heat is given out.
Latent Heat of Vaporisation (Liquid to Gas Change):
- The latent heat of vaporisation of a liquid is the quantity of heat in joules required to convert kilogram of the liquid (at its boiling point) to vapour or gas, without any change in temperature.
Effect of Change of Pressure:
- The physical state of matter can also be changed by changing the pressure.
- Gases can be liquefied by applying pressure and lowering temperature.
- Ammonia gas can be liquefied by applying high pressure and lowering the temperature.
- Solid carbon dioxide (dry ice) is stored under high pressure.