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Matter In Our Surrounding

Tutormate > CBSE Syllabus-Class 9th Chemistry > Matter In Our Surrounding

05 Latent Heat

  • Latent heat is the heat energy which is supplied to change the state of a substance.
  • Latent heat does not cause a rise in temperature of the substance.
  • The latent heat which we supply is used up in overcoming the forces of attraction between the particles of a substance during the change of state.
  • The latent heat does not increase the kinetic energy of the particles of the substance.
  • Since, there is no increase in the kinetic energy of the particles; the temperature of a substance does not rise during the change of state.
  • Latent heat is of two types:
    • Latent heat of fusion
    • Latent heat of vaporisation

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.


  • A change of state directly from solid to gas without changing into liquid state is called sublimation.
  • The common substances which undergo sublimation are Ammonium chloride, Iodine, Camphor, Naphthalene and Anthracene.
  • Solid CO2 gets converted directly to gaseous state on decrease of pressure to  1 atmosphere without coming into liquid state.
  • This is the reason that solid carbon dioxide is also known as dry ice.

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.

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