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Homework Help: Ideal Gas Law and a helium tank

  1. Jan 24, 2009 #1
    1. The problem statement, all variables and given/known data
    Helium in a steel tank is at 250kPa, 300K with a volume of .1m^3. It is used to fill a balloon. When the pressure drops to 150kPa, the flow of helium stops by itself. If all the helium is still at 300k, how big balloon is produced?

    2. Relevant equations
    I used the ideal gas law PV=mRT


    3. The attempt at a solution
    What i did was that i solved for the mass which i got was .04012 and then i used that mass in the ideal gas law with the new pressure of 150kPa to get a new volume of .167 m^3 is this the right approach and answer?
     
  2. jcsd
  3. Jan 25, 2009 #2

    Doc Al

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    Staff: Mentor

    That's a fine approach, but be sure to answer the precise question asked: How big is the balloon?

    Rather than calculate the mass, since it's constant, you could have just used:
    P1V1 = P2V2.
     
  4. Jan 25, 2009 #3
    By asking how big the balloon is doesn't it mean give the volume or what do you think i should put down?
     
  5. Jan 25, 2009 #4

    Doc Al

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    Staff: Mentor

    You want the volume of the balloon, not the total volume.
     
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