Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Kinetic Theory of Gases

  1. May 20, 2007 #1
    1. The problem statement, all variables and given/known data
    1) A container is filled with a mixture of nitrogen and oxygen. What is the ratio of the rms speed of oxygen molecules to that of a notrigen molecules? (molar mass of oxygen = 32 g/mol; molar mass of nitrogen = 28 g/mol)

    2) By what factor does the rms speed of neon molecules increase if their temperature increased by a factor of 4?

    2. Relevant equations

    rms= squared, mean, root.

    1/2mv²=3/2KT where K = 1.83 x 10^-23 (Boltzmann's constant)
    average velocity vectors of molecules = 0

    3. The attempt at a solution

    I'm completely clueless as to how to answer this question.
  2. jcsd
  3. May 20, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper

    (1/2)*m_O*v_O^2=(1/2)*m_N*v_N^2=(3/2)*k*T. Manipulate this to get a ratio of v_O to v_N. I.e. solve for v_O/v_N. Relatively the same approach for 2).
  4. May 20, 2007 #3
    I don't see how you can get rid of the masses and the other variables if they're not constants. The instructions give the molar masses of the gases which are obviously not the same. So, we can't cancel them out when manipulating the equations. May I ask what do you get as an answer?
  5. May 21, 2007 #4


    User Avatar
    Science Advisor
    Homework Helper

    If I divide one expression by the other I get (m_O/m_N)*(v_O/v_N)^2=1. Does that help you to see where to go?
  6. May 21, 2007 #5
    Oh I see thank you, I got it. 0.935 :).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook