# Can a tank of oxygen gas ever be half empty?

Mar 8, 2016

Yes but extremely unlikely.

#### Explanation:

An oxygen contains oxygen molecules. To say that the tank is half empty would mean that all the oxygen molecules only occupy half or less of the tank.

As the movements of the gas molecules are random, it is possible for this to occur. However, the number of oxygen molecules in the tank (which should be in the order of ${10}^{80}$) is sufficiently large that the chance of them all crowding into only one half of the volume of the tank at any instance is

${2}^{- 80} \approx 0.0000000000000000000000827$

$\approx 0$

for practical purposes.

Feb 9, 2017

Yes, but it probably is more a case of semantics.....

#### Explanation:

If you start with a full tank of oxygen, then allow half of its contents to escape into the environment, you will have a tank containing half of the original number of molecules of oxygen.

I would regard that as being "half empty". I don't see why you need all of the molecules to occupy half of the volume of the tank. Why can't all of the (remaining) molecules still occupy all of the volume, but simply exert half of the original pressure?