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Homework Help: A tank of compressed air

  1. Apr 21, 2007 #1
    A tank of compressed air of volume 1.0 m^3 is pressurized to 50 atm at T = 273 K. A valve is opened and air is released until the pressure in the tank is 17 atm. How many air molecules were released?

    I tried this problem using PV = NkT and PV = nRT. I realize the difference in these equations and I was wondering if this in fact the right equations to use? I ran 50 atm through and then 17 atm through. I then subtracted the initial N minus the final N. This didn't work.

    This is what I did:

    (50 atm)(1.0 m^3) = N(1.38e-23)(273)
    N = 1.327e22

    (17)(1.0 m^3) = N(1.38e-23)(273)
    N = 4.512e21

    Nfinal = (1.327e22) - (4.512e21)
    Nfinal = 8.758e21

    This is the wrong answer. What should I do?
  2. jcsd
  3. Apr 21, 2007 #2
    Check your units, can you really use atmospheres with that equation?
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