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Homework Help: PV=nRT question

  1. Jun 23, 2005 #1
    A tank having a volume of .1 m^3 contains helium gas at 150 atm. How many balloons can the tank blow up if each filled balloon is a sphere .3 m in diameter at an absolute pressure of 1.2 atm.

    Here is what I have so far: Assuming no gas gas escapes to the atmosphere during transfer, n is constant. R is constant by definition. Lastly the final volume must be a multiple of (4/3)(pi)(.3/2)^3. But this leaves me with three variables -the volume factor, and the initial and final temperatures...please help... thanks
     
  2. jcsd
  3. Jun 23, 2005 #2

    NateTG

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    You can try assuming the temperature remains constant.
     
  4. Jun 23, 2005 #3
    p1*v1=n*p2*v2

    (assuming t1 = t2)

    v2 = 4/3*pi*(d/2)^3
    with d = 0.3m
    v2 = 0.014 m^3

    n = p1/p2*v1/v2

    n = 150 atm/1.2atm*.1m^3/.014m^3
    n = 884.194
    (0.014 has more numbers after it you'll get this number if u carry them all)

    so I'd say the answer is roughly 884 balloons
     
  5. Jun 24, 2005 #4
    Considering both pressures are absolute, abercrombiems02 arrived nearer to the answer but calculation is wrong(that should give 892.85 balloons).

    When the pressure in the tank falls to 1.2atm absolute, there will be no filling. So you should calculate 148.8*0.1/(1.2*0.014)
     
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