# Do gases have a definite volume?

1. Nov 2, 2009

### mackygood

I've been told that gases take on the volume of whatever container they're in but what about Pv=Nrt ?

Would it be possible that the calculated V is smaller than the container's volume?

Thanks

2. Nov 2, 2009

### Staff: Mentor

That will mean gas is kept in higher pressure - but you can't keep higher pressure if gas is allowed to expand, which will happen if the container is larger.

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methods

3. Nov 2, 2009

### mackygood

Couldn't other variables other than pressure have an impact on the calculated volume of the gas, like the number of moles?

thx

4. Nov 2, 2009

### Staff: Mentor

They do, but they don't change anything.

pV=nRT describes the equilibrium situation, after known number of moles of gas (n) expanded to fill whole container (V). Expansion is fast, but not infinite, so it may happen that gas doesn't occupy whole volume of the container. However, it will not have a constant density then - and you will have troubles defining its volume (in other words - you will have troubles showing where the gas ends, where is the border).

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methods

5. Nov 2, 2009

### mackygood

So as far as I'm concerned, gas volume = container volume? :D

6. Nov 2, 2009

Yes.

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methods

7. Nov 2, 2009

### mackygood

thanks for all your time and help