Latent Heat


Temperature and Heat I - Concepts
Class - 7th DAV Subjects
 
 
Concept Explanation
 

Latent Heat

Latent Heat Of Vaporisation:

The latent heat of vaporisation of a substance is defined as the quantity of heat gained by 1 kg of the substance in changing from liquid to vapour state or from vapour to liquid state at constant temperature.

When you heat a liquid, its molecules start moving faster and gain kinetic energy. This shows as a rise in its temperature. At the boiling point, however, the heat supplied is used by the molecules to break away from the inter-molecular force and change into vapour molecules, rather than to move faster.This is why there is no change in the temperature. The heat required to help the molecules of liquid to overcome the inter-molecular forces and to escape as a vapour molecules is known as the latent heat of vaporisation.

Latent Heat Of Fusion:

The latent heat of fusion is defined as the quantity of heat gained by 1 kg of substance in changing from the solid to liquid at same temperature.

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Sample Questions
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Question : 1

Which of the following are correct ?

(a) The latent heat of fusion is defined as the quantity of heat gained by 1 kg of substance in changing from the solid to liquid .

(b) The latent heat of vaporisation of a substance is defined as the quantity of heat gained by 1 kg of the substance in changing from vapour to liquid state .

(c) The liquid molecules lose the latent heat of fusion to change to solid molecules at the freezing point.

Right Option : C
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Question : 2

Which of the following are correct ?

(a) The latent heat of vaporisation of a substance is defined as the quantity of heat gained by 1 kg of the substance in changing from liquid to vapour state .

(b) The latent heat of fusion is defined as the quantity of heat gained by 1 kg of substance in changing from the solid to liquid .

(c) At the boiling point the heat supplied is used by the molecules to break away from the inter-molecular force and change into vapour molecules.

Right Option : D
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Question : 3

_____________________ is defined as the quantity of heat gained by 1 kg of substance in changing from the solid to liquid at same temperature.

Right Option : A
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