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Homework Help: PV=nRT Question

  1. Apr 6, 2007 #1
    1. The problem statement, all variables and given/known data

    A standard cylinder of oxygen used in a hospital has gauge pressure = 2.0E3 psi (1.38E4 kPa) and
    volume = 16 L (0.016 m3) at T = 295 K. How long will the cylinder last if the flow rate, measured at atmospheric pressure, is
    constant at 1.8 L/min?

    2. Relevant equations


    3. The attempt at a solution

    I assume it's not as simple as 16/1.8?

    I used PV=(m/M)RT to solve for mass, but that got me no where.
  2. jcsd
  3. Apr 6, 2007 #2


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    The gas in the cylinder is under pressure. So it is equivalent to many more liters at atomospheric pressure. Find out how many and then it is as simple as you think.
  4. Apr 6, 2007 #3
    So nRT is constant correct?

    So (PV)_inside=(PV)_outside?


    Solve for V, then use that in t=V/flowrate?

  5. Apr 6, 2007 #4
    you may have to use calculus to solve this
  6. Apr 6, 2007 #5
    No, it's the lowest level physics class.
  7. Apr 6, 2007 #6


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    Right. Just assume the gas is delivered at atmospheric pressure and outside temperature.
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