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### Topic: Expansion of Ideal Gas in a Vacuum (Thermodynamics)  (Read 4768 times)

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#### neuroid

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##### Expansion of Ideal Gas in a Vacuum (Thermodynamics)
« on: September 25, 2012, 08:51:06 AM »
After you close the hatch on the international space station, the airlock region is a
nearly perfect vacuum, so you need to start refilling that region with air.  Suppose that
you do so by opening up a 10.0 liter tank of 5.00 atm air, allowing the air to expand so
that it now takes up a total volume (tank+ airlock) of 2000 liters.  Take the air to be an
ideal gas and assume that the process is isothermal (carried out at constant temperature).
What are q and w for this process?  What would q_rev and w_rev have been for the same net

This question has been giving me some problems because it only gives me P_initial and ΔV. I can't calculate w using w = -PΔV because pressure isn't constant (unless w = -ΔPΔV is a viable equation). I can't calculate w_rev, either, through -nRT ln (V_f/V_i) because I don't know the number of moles or the temperature.

Also, how would you calculate isothermal q if it isn't during a phase change? Is this process adiabatic?

Thank you to anyone who offers help.

#### Jorriss

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##### Re: Expansion of Ideal Gas in a Vacuum (Thermodynamics)
« Reply #1 on: September 25, 2012, 04:23:42 PM »
Intuitively, do you have any expectation for what the work will be? As the guy expands, what is it doing work against?

#### TheStapler

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##### Re: Expansion of Ideal Gas in a Vacuum (Thermodynamics)
« Reply #2 on: September 30, 2012, 10:16:29 PM »
Could you elaborate on that answer? I tried to help, but I'm not certain of the Qrev or Wrev for this process, I understand that for Q and W, it's expanding against the vacuum, but the reversible process confuses me too.

#### TheStapler

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##### Re: Expansion of Ideal Gas in a Vacuum (Thermodynamics)
« Reply #3 on: September 30, 2012, 11:23:09 PM »
It's PV BROOOOOOO!

#### alibek@assilov

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##### Re: Expansion of Ideal Gas in a Vacuum (Thermodynamics)
« Reply #4 on: October 01, 2012, 08:44:36 AM »
Use the following equations

P1V1 = P2V2

P1/P2 = T1/T2

P1 = 5 atm, P2 = 1 atm

V1 = 10 litre, V2 = 2000 litre