Latent heat
Normally, when heat is given to a substance, then its temperature rises. This, however, is not so when a change of state of a substance takes place. Because when heat is given to change the physical state of a substance (from solid to liquid or liquid to gas), there is no rise in temperature of the substance. The heat energy which has to be supplied to change the state of a substance is called its latent heat. Latent heat does not raise (or increase) the temperature. But latent heat has always to be supplied to change the state of a substance. The word 'latent' means 'hidden'. It is called latent heat because it becomes hidden in the substance undergoing the change of state, and does not show its presence by raising the temperature. So, the latent heat which is given to change the state of a substance cannot be detected by a thermometer. Let us see why latent heat does not cause a rise in temperature of the substance.
Every substance (solid or liquid) has some forces of attraction between its particles which hold them together. Now, if a substance has to change its state, then it is necessary to overcome (or break) these forces of attraction between its particles. 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. And 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 :
1.Latent heat of fusion, and
2.Latent heat of vaporisation.
The heat required to convert a solid into the liquid state is called latent heat of fusion (or latent heat of melting). And the heat required to convert a liquid into the vapour state (or gas) is called latent heat of vaporisation. We will discuss both the types of latent heats in somewhat detail, one by one.
Notes
Sound - Notes
3. 2. Liquid to Gas Change : Boiling (or Vaporisation)
Show Notes
4. 2. Latent Heat of Vaporisation (Liquid to Gas Change)
Show Notes
5. Effect of 'Heating' and 'Cooling' on a Saturated Solution
Show Notes
6. Classification Of Matter As Solids, Liquids And Gases
Show Notes
8. Why Solids, Liquids and Gases Have Different Properties
Show Notes
14. 2. The Particles of Matter have Spaces Between Them
Show Notes
15. 1. Solid to Liquid Change : Melting
Show Notes
16. 3. Gas to Liquid Change : Condensation
Show Notes
20. 1. Latent Heat of Fusion (Solid to Liquid Change)
Show Notes
24. 1. The Particles of Matter are Very, Very Small
Show Notes
26. 4. The Particles of Matter Attract Each Other
Show Notes
28. 3. The Particles of Matter are Constantly Moving
Show Notes
29. Characteristics of Particles of Matter
Show Notes
30. 4. Liquid to Solid Change : Freezing
Show Notes
31. Two More States of Matter : Plasma and Bose-Einstein Condensate
Show Notes
38. The Common Unit Of Temperature and Si Unit Of Temperatre
Show Notes
39. To Show That Solids and Liquids Cannot be Compressed but Gases Can be Compressed Easily
Show Notes
44. To Show that Liquids do not have a Fixed Shape but they have a Fixed Volume
Show Notes
45. To Show the Presence of Water Vapour in Air
Show Notes
49. Gases Can be Liquefied by Applying Pressure and Lowering Temperature
Show Notes
50. To Show that Gases do not have a Fixed Shape or a Fixed Volume
Show Notes
