Gas pressures with (hypothetical) filter

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SUMMARY

This discussion centers on the behavior of gases in two connected containers, specifically when a hypothetical filter allows only one type of gas to pass. In the scenario presented, Container A holds 3 moles each of Ideal Gas A and Ideal Gas B, while Container B holds none. When a filter that permits only Gas B to pass is introduced, Gas A remains in Container A, and Gas B moves to Container B until the partial pressures equalize. The conversation highlights the importance of understanding gas laws and the implications of filters on gas distribution and entropy.

PREREQUISITES
  • Understanding of Ideal Gas Law
  • Knowledge of gas pressure and partial pressure concepts
  • Familiarity with entropy and thermodynamic principles
  • Basic grasp of Maxwell's demon thought experiment
NEXT STEPS
  • Research the Ideal Gas Law and its applications
  • Explore the concept of partial pressures in gas mixtures
  • Study the implications of entropy in thermodynamic systems
  • Investigate Maxwell's demon and its relevance to thermodynamics
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This discussion is beneficial for physics students, chemists, and anyone interested in thermodynamics and gas behavior, particularly in scenarios involving filters and gas mixtures.

funkyfreshcecil
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Imagine I have 2 constant-volume, constant-temperature containers. Container A has a volume of 10 L and one Container B has a volume of 5 L.

My hypothetical gases Ideal Gas A and Ideal Gas B have the same properties as each other (temperature, mass, energy, heat capacity, blah blah blah).

If I insert 3 moles of Ideal Gas A and 3 moles of Ideal Gas B into Container A and connect the two containers, I'd expect the pressure to equalize between the containers, and the final distribution of the gases to be
Container A: 2 moles Gas A, 2 moles Gas B
Container B: 1 mole Gas A, 1 mole Gas B

makes sense.

Now, I restart the experiment, but this time I've placed a magic filter (possibly controlled by a demon) that only allows Gas B to pass, and insert it the connection between the two containers.

What would the distribution of the gases be?

Obviously all of Gas A stays in Container A, thanks to the filter.

Would Gas B move to Container B until the total pressure was equal between the two containers? Or would the partial pressure of Gas B move it until the Gas B pressure was equal. Or does it have to do with the number of moles in each container. Or...?
Thanks for any insight anyone who understands ideal gas laws can give!
 
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Doesn't this depend on the properties of this magic filter? (e.g. can it do work?)
 
Good point.

This magic filter doesn't apply any forces to the gas any more than the container walls do -- it's a Maxwell's demon-ish type filter that simply allows the passage of one type of gas particle but not the other.

For example if the two gases have molecules of different size, and the filter has holes that allow one size particle through and not the other.

Would that count as doing work? I don't think it's adding energy to the system if that happens. It's definitely messing with the entropy though.If no work were being done by the filter, my intuition says that the two containers should still equalize in pressure. Or is it just the case that each gas equalizes in pressure, if it can?
Thanks for your quick response.
 

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