Gas expansion limit?

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TL;DR
Now that I've had my coffee, I'll mention the problem with using a balloon in this sort of thought-experiment is any real balloon exerts some pressure on the gas (i.e. the gas is held in by more than just atmospheric pressure). That's why when teaching thermodynamics of gases problems start with "a frictionless piston filled with an an ideal gas". The container itself should not apply any forces on the gas.

OBTW, your weather balloon heading to the stratosphere will also experience a drop in temperature, which will work in the opposite direction as the decreased pressure.

But, absent a balloon, your Helium gas would continue to expand "forever" to an "infinite" volume. Unless you start to consider the very weak, but non-zero, forces of attraction between the He atoms ("London Dispersion Forces") and gravity.
 
TL;DR
Now that I've had my coffee, I'll mention the problem with using a balloon in this sort of thought-experiment is any real balloon exerts some pressure on the gas (i.e. the gas is held in by more than just atmospheric pressure). That's why when teaching thermodynamics of gases problems start with "a frictionless piston filled with an an ideal gas". The container itself should not apply any forces on the gas.

OBTW, your weather balloon heading to the stratosphere will also experience a drop in temperature, which will work in the opposite direction as the decreased pressure.

But, absent a balloon, your Helium gas would continue to expand "forever" to an "infinite" volume. Unless you start to consider the very weak, but non-zero, forces of attraction between the He atoms ("London Dispersion Forces") and gravity.
Once it reached space would it not just stay at whatever volume it had expanded to while there was still atmospheric pressure?
 
Once it reached space would it not just stay at whatever volume it had expanded to while there was still atmospheric pressure?
Not really.
Each molecule would have a speed which is function of temperature (thermodynamical temperature) which would be non zero if T>0K which is -273 C (wont calculate in F) so as long as you are above absolute 0 degrees ... the gas will keep expanding.
Especially if helium. I am not considering sun, earth and moon gravitational effect here but they are pretty small compared to molecular speeds ... :) at typical space temps in sun light.
 
Im impressed all but one kept things on a serious nature. Hope that does nto keep teh OP from asking other things.
 
Not really.
Each molecule would have a speed which is function of temperature (thermodynamical temperature) which would be non zero if T>0K which is -273 C (wont calculate in F) so as long as you are above absolute 0 degrees ... the gas will keep expanding.

Well... you could argue that there is a practical limit at which it ceases to be "expanding gas" and becomes "loose individual molecules scattered around in vacuum".
 
Well... you could argue that there is a practical limit at which it ceases to be "expanding gas" and becomes "loose individual molecules scattered around in vacuum".
Yes, and also that at the end they would stay in loose vicinity of earth since, otherwise, we would loose the whole atmosphere and end up like the moon ....
 
Yes, and also that at the end they would stay in loose vicinity of earth since, otherwise, we would loose the whole atmosphere and end up like the moon ....

Hmm, I guess OP did say "Earth normal conditions".
 
Hmm, I guess OP did say "Earth normal conditions".
Yeah, but nothing is normal on earth this year. So I wouldn't be surprised in 2020 to see the lift bag to go from 33fsw all the way to the surface and then keep going up into the stratosphere, where it finally burst, sending back down a cascade of air that somehow turned toxic and killed half the planet. Something about the butterfly effect in 2020.
 
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