Question Video: Predicting the Diffusion of Two Different Gases after a Wall Is Removed | Nagwa Question Video: Predicting the Diffusion of Two Different Gases after a Wall Is Removed | Nagwa

Question Video: Predicting the Diffusion of Two Different Gases after a Wall Is Removed Physics • Second Year of Secondary School

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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?

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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.

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