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Expansion of balloon

  1. Dec 3, 2014 #1
    If I heat a rubber balloon filled with helium slowly and if the balloon is fully expandable and (the balloon) can be assumed to require no energy in its expansion,what type of thermodynamic process is taking place? Is it isobaric?
    Since the balloon expands the pressure exerted by the gas on balloon should increase. Then how can it be isobaric?
    It can't be isochoric nor isothermal.
    It is either adiabatic or isobaric.
     
  2. jcsd
  3. Dec 3, 2014 #2
    its called free expansion . work done by the balloon is zero and so is the change in heat . this results into no change in internal energy by the first law of thermodynamics .
     
  4. Dec 3, 2014 #3
    It's given isobaric... This concept came in IIT
    Exam.... The toughest exam in India for admission to B.tech. IIT IS THE MOST REPUTED COLLEGE IN MY COUNTRY.
     
  5. Dec 3, 2014 #4
    Yes, it's isobaric. If the balloon is fully expandable (i.e., doesn't develop significant tension as it expands), the pressure inside the balloon is always nearly equal to the pressure outside the balloon. And, the pressure outside the balloon is 1 atm. (constant). So the pressure inside the balloon is constant at about 1 atm, and the process is isobaric. The key to all this is that the balloon membrane doesn't develop significant tension.

    Chet
     
  6. Dec 3, 2014 #5
    If rubber tension is negligible it is isobaric otherwise we can consider P=f(V), and f depend on rubber specification and balloon dimensions.

    https://physicsforums-bernhardtmediall.netdna-ssl.com/data/attachments/59/59222-ef0af70f5c70ec1351bf0a5e6d506887.jpg [Broken] I
     

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  7. Dec 3, 2014 #6
    Actually, it would be the pressure difference across the rubber membrane ΔP that you can calculate from the rubber properties and the balloon shape.

    Chet
     
    Last edited by a moderator: May 7, 2017
  8. Dec 4, 2014 #7
    when you are heating a gas its randomness increases so it will collidewith the walls of the balloon more freaquently. hence pressure inside th balloon should increase right?
     
  9. Dec 4, 2014 #8
    Not if volume increases so that the pressure matches the outside pressure.

    Chet
     
  10. Dec 4, 2014 #9
    so you mean that the area of contact increases and since P=F/A pressure increase gets countered by expansion of balloon.
     
  11. Dec 4, 2014 #10
    No. Pressure stays the same. You're familiar with the ideal gas law, correct?
     
  12. Dec 4, 2014 #11
    Pv=nRT. as volume temperature of balloon increases pressure should increase.
    if pressure exerted by gas on balloon doesnt change, how does it expand.
     
  13. Dec 4, 2014 #12
    From your understanding of mathematics, if the volume v increases in direct proportion to the temperature T, how does the pressure vary?
    We already said the we are looking at a limiting case in which the stiffness of the balloon membrane is negligible. Under these circumstances, the pressure inside the balloon must match the pressure outside the balloon, and the pressure outside the balloon is constant at 1 atm.

    Chet
     
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