Video Transcript
Two gases are held in adjacent containers of equal volume. If the wall separating the containers is removed, in which direction would the
particles of the gas shown in orange diffuse? (A) They will diffuse toward the left. (B) They will diffuse toward the right. (C) They will diffuse in all directions. Or (D) they will not diffuse.
To begin, let’s remind ourselves about diffusion. Diffusion is a process where particles in a container move from a region of greater
concentration to lesser concentration as a consequence of Brownian motion. In other words, the particles tend to spread out evenly across the volume they’re
contained in.
Imagine, for example, that we have a container that holds some number of gas
particles. And suppose that the gas has just been introduced to the container on the right
end. This drawing represents the particles in the container a short time later. So notice that all the particles are bunched together on the right. When this is the case, the particles are at a relatively high concentration over
here, because they’re only occupying a small volume within the container. But over time, these particles will all undergo Brownian motion, meaning they’ll move
in seemingly random ways due to collisions with other particles. This causes the particles to move from a greater concentration, where they’re all
bunched up at the right-hand side, to a lesser concentration, where they’re evenly
spread throughout the container. This is diffusion.
Okay, now that we’ve recapped diffusion, let’s return to the question we’ve been
asked. We need to work out the direction in which the orange gas particles will diffuse if
the wall in the middle of the container is removed. Just after the wall has been removed, the container will look like this. The concentration of orange particles on the right-hand side is very great. And the concentration of orange particles on the left-hand side is zero. But we know that as time goes on, the orange particles will diffuse from a region of
greater concentration to lesser concentration until they’re spread evenly throughout
the container, just like we described before.
It’s important to note that the different colored particles represent different kinds
of gases. When this is the case, we assume that the different gases will diffuse independently
of each other. So the fact that there is a high concentration of these other particles on the
left-hand side of the container has no impact on the diffusion of the orange
particles. In fact, for the purposes of this question, we can remove the other particles from
the diagram altogether.
Now, it should be much easier to see how the orange particles will diffuse. They’ll diffuse toward the left, where there is a lower concentration of orange
particles until they’re evenly spread throughout the container. This corresponds to option (A), so we know that (A) is the correct answer. After the wall separating the containers is removed, the orange particles will
diffuse toward the left.
