Effusion
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.
