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What is Diffusion?

Spreading out and Mixing of one substance with other is called Diffusion
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It happens in all forms of matter - Solids, Liquids and Gases

It is fastest in gases and slowest in solids

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Examples of Diffusion in Gases

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Example 1

  • We take 2 gas jars, one contains brown coloured bromine gas and other containing air (which is colourless)
  • Now we invert gas jar containing bromine gas over gas jar containing air
  • After some time, we observe both gas jar become brown in color
  • This is because of diffusion (spreading out or mixing) bromine gas in air


Example 2

The smell of cooked food reaches our nose because of the diffusion of food gas in the air


Example 3

The smell of perfume/incense stick (agarbatti) reaches us because of diffusion of perfume gas in the air

Examples of Diffusion of Liquids


Example 1

If a drop of ink is put in a jar of water, the colour soon spreads to the whole of the jar

This is due to the diffusion of ink particles i n water

Example 2

If a crystal of Potassium Permanganate is put in a jar of water

Then whole water soon turns into a purple colour

This is due to the diffusion of potassium permanganate in water

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Example 3

Aquatic Animals used dissolved oxygen in the water to breathe

Aquatic plants use dissolved carbon dioxide in water for photosynthesis

This is due to the diffusion of oxygen and carbon dioxide particles in water

Examples of Diffusion in Solids

Diffusion in solids is slowest and takes a lot of time



If we write something on the blackboard and do not erase it for a long period of time

The chalk particles get diffused with particles of blackboard

Hence we find it difficult to erase

Example 2

If 2 metal blocks are bound together and kept for a few years

Particles of both box mix with each other

Comparison - Diffusion in Solids, Liquids and Gases

Solids Liquid Gases
Diffusion is slowest in Solids Diffusion is fast compared to solids but slow compared to liquids Diffusion is fastest in gases

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CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Accounts and English at Teachoo