The Passage of gases from a high-pressure zone to a low-pressure zone through a fine pore is called an effusion.

Take a balloon and fill it with air or helium. Stick a piece of scotch tape on the balloon. Now, make a small pore on the balloon through the scotch tape and see what happens. The air from the balloon will come out through the hole with force (Don't try it without the scotch tape; the balloon will burst). Air pressure inside the balloon was higher than outside. So, when the air found the hole, the air from the balloon rushed towards the low pressure region. It is effusion. Like the rate of diffusion if heat is applied, the rate of effusion increases. If heat is applied, the rate of effusion increases very much like the rate of diffusion. 

We use CNG (compressed natural gas) as fuel in our vehicles. Basically, it is compressed methane gas at high pressure. When we run our vehicle, this gas comes out of the cylinder with high pressure and runs the engine. This is also an effusion of gas.

Again, propane and butane gases are compressed at high pressure into liquid and put into cylinders to use them for cooking in households. When we open the cylinder for cooking, it comes out in gaseous form with pressure. It is another example of effusion.

Effusion and diffusion are by nature, the same kind of actions. The basic difference between them is, effusion requires the presence of pressure but diffusion does not depend on pressure. 

In diffusion, solids, liquids or gases matter spread around in a suitable medium but in effusion, only gas comes out through a fine hole from the container. If we open the cylinder but do not ignite our cooker, the gas from the cylinder will just come out and mix with air. This is effusion. Then, the gas that comes out would spread around the room, which is diffusion. Therefore, both actions may take place one after another.


Secondary Chemistry

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