Expanding gas cools

[Cofo]

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Why is it true that when a gas expands, it cools down (decreases in temperature)?

Is it because its collisions with other gas molecules (or a container wall) decreases, thereby reducing the recoil and kinetic energy (temperature) of the gas?

 

[Cool Beans]

This is only true for real gases (not ideal gases). Real gases have intermolecular attractive forces that have to be overcome as the gas expands (as the molecules spread out from each other) and this requires energy. Therefore real gases lose energy as they expand and this is reflected in a decrease in the temperature.

 

[Cofo]

This is only true for real gases (not ideal gases). Real gases have intermolecular attractive forces that have to be overcome as the gas expands (as the molecules spread out from each other) and this requires energy. Therefore real gases lose energy as they expand and this is reflected in a decrease in the temperature.

Gotcha, thanks Chad. You rock.