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Homework Help: Atoms in a Helium Balloon.

  1. Nov 28, 2007 #1
    1. The problem statement, all variables and given/known data

    (a) How many atoms of helium gas fill a balloon of diameter 29.4 cm at 23.5°C and 1.00 atm?
    (b) What is the average kinetic energy of the helium atoms?
    (c) What is the root-mean-square speed of the helium atoms?


    2. Relevant equations

    P=2/3[N/V][1/2mv^2]
    v=srt(3RT/M)
    R=8.31
    T=23.5 degrees celcius = 296.5K
    M(He)=4.0026g/mol
    E(int)=3/2nRT
    Avogadros #: 6.0221415 × 10^23

    3. The attempt at a solution
    (a)I dont know how to find the # of molecules. I know I need Avogadros #.
    (b)To solve this, dont I need the first one solved?
    (c) v=sqrt((3(8.31)(296.5K))/4.0026 g/mol) = 42.97m/s = 0.0429km/s (which is wrong coz I did this part first)
     
  2. jcsd
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