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Homework Help: Speed of a Molecule Question

  1. Oct 15, 2009 #1
    1. The problem statement, all variables and given/known data

    Consider a gas-phase N2 molecule. It's RMS speed is given by

    Vrms = (3kT/m)^(1/2)

    What speed would the gas molecule have if it had the same energy as a photon of the following wavelengths of IR, visible, UV and X-Ray electromagnetic radiation?

    lambda = 1.000E4nm, 500nm, 100nm, 0.10nm

    2. Relevant equations

    E=hc, E=hc/lambda E = (mv^2)/2 , not sure if we should use lambda = h / p (momentum)

    3. The attempt at a solution

    So I don't know how to use the Vrms equation that is given in the problem. I am not sure if we need to use it at all (Btw, this in the first problem set of my pchem class so it should be pretty easy, I am just not sure if I am doing it right).

    E = hc/lambda, using this equation we can find the energy of the gas molecule if it had the wavelength given in the problem.

    Once we find the energy E we can use KE = 1/2mv^2 to some for v.

    I am not sure if we are supposed to use this method or use the Debroglie equation where lambda = h / mv and solve for velocity that way.

    Any thoughts?
  2. jcsd
  3. Oct 17, 2009 #2


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    Staff Emeritus
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    That is how I would solve it. Not sure why they bothered with the vrms equation :confused:
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