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Homework Help: Molecular Flux of a gas

  1. May 14, 2013 #1
    1. The problem statement, all variables and given/known data
    What is the molecular flux of argon gas, molar mass 18 g/mol, with density 0.73 kg/m3 and temperature 300 K? Answer: 3.6×10^27 collisions/m^2s

    2. Relevant equations
    I actually have no idea

    3. The attempt at a solution
    I can't find any reference to molecular flux in my notes or 2 physics text books, an equation would be appreciated.
  2. jcsd
  3. May 14, 2013 #2


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  4. May 14, 2013 #3
    Thank you for the link. If I read it correctly, flux = .25*(N/V)*√(8kT/([itex]\pi[/itex]m)

    however, the density in the problem is given in kg/m^3 while the equation calls for the density based on the number of molecules, which is not given. It's probably an algebra problem now, but I'm also unsure with what to do with the given molar mass.
  5. May 15, 2013 #4


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    It is easy to get the number density of molecules from the mass density and molar mass.
    Molar mass is 18 g/mol=0.018 kg/mol. 1 mol gas contains NA (Avogadro Number) molecules, so the mass of a single molecule is 0.018/NA kg.
    The mass density is 0.73 kg/m3, so the mass of 1 m3 gas is 0.73 kg. How many molecule is it ?

  6. May 15, 2013 #5
    Thanks, I got it now.
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