Ans : Diffusion :
The spreading of a substance through medium like air or liquid is called diffusion. The rate of diffusion of a substance depends upon its molar mass or density.
Example :
When perfume is sprayed in the room it spreads in the whole room because of movement of molecules.
Graham’s Law of Diffusion :
In 1846 Thomas Graham put forward his law of diffusion.
Statement :
“The rate of diffusion of a gas is inversely proportional to the square root of its molar mass or density.
Explanation :
Lighter gases can diffuse faster than heavier gases. For example hydrogen gas diffuses four times faster than the oxygen gas.
Diffusion in liquids :
Liquid is intermediate between gaseous & solid states. Like gases liquid molecules are able to move & thus flow & diffuse. The rate of movement of liquid molecules is slower than gases & hence they diffuse slower than gases.
Diffusion in gases :
If molecules of gas are set free in a big container they will quickly spread around in the available space due to their kinetic energy.
This spreading of gas is called diffusion in gas.