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Homework Help: A Sealed Bottle of Gases

  1. Dec 5, 2013 #1
    1. The problem statement, all variables and given/known data
    A sealed bottle at 1 atm of pressure holds 1 mole of neon and 1 mole of argon gas at a temperature of 295K. The curves in the Figure (http://phlnx3.pas.rochester.edu/webwork2_files/CAPA_Graphics/Gtype43/prob01a.gif) show the distributions of velocities of the molecules of each gas.
    Find the number of molecules of argon which have velocities between 250 m/s and 500 m/s.

    2. Relevant equations
    KE = (3/2)kT
    P(v) dv [itex]\propto[/itex] 4πv^2 e^((-(1/2)mv^2)/kT) dv
    Molar Mass of Argon = 0.03995 kg/mol

    3. The attempt at a solution
    Totally lost on how to set this one up. I get that I need some sort of bound on the probability of finding Argon between 250 and 500 m/s, and from there I can get an actual number, but for now I'm somewhat lost.
    The graph might be giving me the answer right in front of me but I'm also having a hard time reading it (it doesn't help that it's not labeled which curve is which element...).
  2. jcsd
  3. Dec 5, 2013 #2
    Argon has a higher molar mass than neon. What does that tell you about which curve is which? As a last resort, you can count area under the curve from 250 to 500.
  4. Dec 5, 2013 #3
    It should be the top curve since vrms would be lower than Neon. I thought it would be harder than that but I just manually calculated the area and got the right answer. Guess I was overthinking it. Thanks!
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