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Ideal gas question on oxygen

  1. May 7, 2006 #1
    A standard cylinder of oxygen used in a hospital has the following characteristics at room temperature (295 K): gauge pressure = 13,800 kPa (2000 psi), volume = 16 L (0.016 m^3). How long will the cylinder last if the flow rate, measured at atmospheric pressure, is constant at 2.4 liters/min?

    I tried to find the volume (in liters) at atmospheric pressure. It didn't come out right.

    Since nRT is constant do I need to find the number of moles?

    Am I taking the wrong approach?
     
  2. jcsd
  3. May 7, 2006 #2

    Hootenanny

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    Assuming temperature is constant you could use Boyle's law.

    ~H
     
  4. May 7, 2006 #3
    Does that work for gauge pressure?

    Thank you.
     
  5. May 7, 2006 #4

    Hootenanny

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    You must first convert it to absolute pressure, remember;

    [tex]P_{gauge} = P_{abs} - P_{atm}[/tex]

    ~H
     
  6. May 7, 2006 #5

    LeonhardEuler

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    Just add atmospheric pressure to the guage pressure to get absolute pressure.
     
  7. May 11, 2006 #6
    P absolute = P gauge + P atmospheric

    = 13,800 kPa + 101 kPa

    = 13,901 kPa

    PV = k

    If I don't need to know k, how to I use the equation?
     
  8. May 11, 2006 #7

    Hootenanny

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    If you know the pV is constant you can make an equality with respect to the intial and final pressures and volumes, thus;

    [tex]p_{i}V_{i} = p_{f}V_{f}[/tex]

    ~H
     
  9. May 11, 2006 #8
    Many thanks for all of the help.
     
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