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Q & A: size of gas molecules

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Most recent answer: 04/08/2020
Is it true that the size of molecules is so small that they don't contribute to the volume of the gas
- cindy (age 18)
south Africa

At standard temperature and pressure, the gas molecules do indeed take up a very small fraction of the gas volume. You can tell that because when the gas is cooled down to make a liquid, with the molecules packed in next to each other, the liquid typically takes up about 1/1000 of the volume of the gas. Of course that number depends not only on the pressure and temperature but also on the type of molecule.

Mike W.

(published on 05/08/2015)

Follow-Up #1: how masks work

How small gas molecules if you were to make a gas mask?
- Shera Raisen (age 56)

It sounds like you're thinking that gas masks work by having such small holes that bigger molecules can't get through. That sounds reasonable, but it's not actually how they work, since it would be very hard to breathe through anything like that.

An N95 mask, for example, works by having many little fibers that small particles stick to. Larger particles tend to just bang into the fibers rather than following the gas flow. Smaller particles diffuse around so much just from random thermal motions that they also tend to bump into fiber and get stuck. Mi-suze particles (around 0.3 microns) are harder to trap, but mostly still get caught by a good mask.

Real gas masks also contain some material (sometimes charcoal) that can catch individual molecules of some harmful gases, not just the multi-molecule particles that N95's catch.

I'm not sure that answers your question, but it may be of interest these days.

Mike W.


(published on 04/08/2020)

Follow-up on this answer.