Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Ideal gasses and the law

  1. Feb 6, 2008 #1
    1. The problem statement, all variables and given/known data
    I have a ballon on the ground, where it is 20 degrees celcius, and it has a volume of 5L (it is filled with helium). The pressure at the ground is 1 atmosphere. The ballon itself (without helium) weighs 0.1 kg.

    I find the force that makes the ballon go up to be:

    F_up = (m_air)*g = 58.96 N

    F_down = (m_Helium + m_ballon) * g = 9.13 N

    So the ballon will go up.

    I can also find the number of Helium-moles from n = m/M, and I find that n = 207 moles.

    3. The attempt at a solution
    My questions are:

    As the ballon goes up, the pressure goes down and so does the temperature. I want to know, which parametres are affected by this?

    The density of the helium? Yes, because density is written as "rho" = M*p/(R*T), so this changes.

    The volume of the helium? yes, this changes as well.

    The number of helium-moles? No, this is constant too.

    The mass of the helium? Yes, this gets smaller when the temperature goes down since "rho" = m/V.

    The pressure inside the balloon? No, this stays the same.

    Can you guys please confirm this?
     
    Last edited: Feb 6, 2008
  2. jcsd
  3. Feb 6, 2008 #2
    - the pressure of the balloon is constant also, right?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook