Difference Between Diffusion and Effusion

Diffusion vs Effusion

Diffusion and effusion are properties of gases and students confuse a lot between these properties because of similar sounding names. Though both diffusion and effusion involve gases, and how gases flow and on what factors this flow rate depends, the two phenomenons are different from one another and the manner in which they are different will be discussed in this article.

The easiest way to learn about diffusion is to understand the manner in which a person wearing a perfume enters a room and the fragrance travels in the room. The person closest to him gets to smell the perfume earliest while the person sitting farthest from the person wearing perfume smells the perfume in the end. This is because of diffusion of the molecules of perfume in the room. Diffusion of gases is a natural phenomenon and it carries on in our atmosphere all the time. When you light a matchstick, you get a pungent smell but within a moment this smell subsides. Why? Because the foul smelling gases quickly diffuse in the atmosphere.

Effusion is another property of gases which allows gasses to move from areas of high pressure to areas of low pressure through a pinhole. Grahams Law states that rate of flow of different gases from a pinhole container are inversely proportional to the square root of their densities. If we know effusion rates of two different gases and know the density or molecular weight of one gas, we can easily calculate the molecular weight of the unknown gas.


Diffusion vs. Effusion

Both diffusion and effusion are terms in chemistry and describe the properties of gases. Whereas diffusion talks about ability of gases to mix with each other, effusion describes different rates at which gases pass through a pinhole from an area of high pressure to an area of low pressure. Both processes are governed by Graham’s Laws.