Graham's law, diffusion, effusion

[reising1]

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Diffusion can be demonstrated by having two different gases at two ends of a tube and watching when they reach and precipitate. Effusion can be demonstrated by placing a gas in one side of a container which is connected to another side by a tiny hole.

Graham's law is also known as the law of effusion. However, it is always used to solve diffusion problems (ex. at what position do the gases meet).

So now you can see why this is a little bit confusing...

What's going on here?

 

[twofac3]

It is applicable to both scenarios. Grahms law just states that the speed at which a molecule moves is related inversely to the square root of its mass. r1/r2 = sqrt(M2/M1) This is applicable for both effusion, AND diffusion.

 

[twofac3]

It is important to note that larger molecules will move more slowly, and vice versa.

 

[reising1]

What if it's effusion with a single gas? How can we find the speed?