# Behavior of Air Molecules when Heated

1. Oct 7, 2013

The problem statement, all variables and given/known data

Some gas is heated in a sealed container. How do the average distance between the gas molecules, and the frequency of the molecules' collision with the walls, change when the container

(A) has a fixed volume, and
(B) is allowed to expand outwards?

The attempt at a solution

(A) Container has a fixed volume
1) I am not sure about the average distance. The molecules move faster, but they are kept in a fixed space. Does that mean that the average distance remains unchanged?
2) The frequency of the molecules' collision with the walls will increase, since the molecules are moving faster.

(B) Container is allowed to expand
1) Will the average distance increase since there is more space for them to move?
2) The frequency of the molecules' collision will remain unchanged?

Will appreciate any guidance. Thank you!

Last edited: Oct 8, 2013
2. Oct 8, 2013

### Staff: Mentor

1) I agree with your thinking.
2) I agree with your thinking. Hotter molecules move faster.

1) I agree with your thinking.
2) We aren't told how much the container is allowed to expand. Suppose just 1% expansion. If we increase the temp by a large amount then collision frequency will be more. So I think we can't say anything definite about the collision frequency, other than it can be expected to change.