1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Thermodynamics Pressure Calculation

  1. Sep 19, 2012 #1
    A spherical balloon is filled with helium atoms (Note: 1 atm = 101.3 kPa).
    What is the total translational KE of the atoms if the balloon has a diameter 26.0 cm at 46.0 °C and the pressure inside the balloon is 121.6 kPa?

    The answer is 1680J but I can't get it.

    I used KE=3/2kT (in J/molecule) and then multiplied that number by the number of molecules PV=nRT. Am I working it out wrong or using the wrong numbers (like should I use Kelvin for temperatures)?

    KE=3/2*1.38x10^-23*46 =2.4x10^21
    V= 4/3*pi *radius^3 =4/3*pi*(13/100)^3 =9.2*10^-3
    n=PV/RT = (121.6*9.2x10^-3)/(8.314*(46+273)) Not sure if I should use Kelvin here
    n= 4.22x10^-4
    KE*n = 2.4x10^21* 4.22x10^-4=1x10^18J (which is so off the right answer).
     
  2. jcsd
  3. Sep 19, 2012 #2
    Oops. Somehow my thread got posted twice...!?! Sorry...
    I dunno how to delete...
     
  4. Sep 19, 2012 #3
    never mind. I got it. Thanks for looking anyway.
     
  5. Sep 19, 2012 #4

    Borek

    User Avatar

    Staff: Mentor

    Click on Edit button, look for Delete button.

    Note that Edit is active only for a limited period of time, if you will wait for too long, posts is no longer editable.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Thermodynamics Pressure Calculation
  1. Pressure Calculation (Replies: 11)

Loading...