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Homework Help: Thermodynamics nitrogen molecules help

  1. Apr 29, 2008 #1
    1. The problem statement, all variables and given/known data

    At 100 Celcius the rms speed of nitrogen molecules is 576 m/s. Nitrogen at 100 Celcius and a pressure of 2.0 atm is held in a container with a 10cm x 10cm square wall.

    2. Relevant equations

    rate of collisions: N_coll/ [tex]\Delta[/tex]t = (N*A*v_x)/(2V) (this is from my textbook)
    ideal gas law: N = PV/k_bT (k_b == boltzmann constant)

    3. The attempt at a solution

    I took that equation and applied the ideal gas law to replace N,
    number of collisions = (P*A*v_x)/(2*k_b*T)
    = (2 * 101325 Pa)(.1*.1 m^2)(576m/s) / ( 2 * 1.38 * 10^-23 * (100+273.15) )

    after plugging in the numbers I got 1.13 * 10^26, but that's wrong. I'm not sure why.

    Last edited: Apr 29, 2008
  2. jcsd
  3. Apr 30, 2008 #2
    The equation that you use for the rate of collisions is asking for v_x, not v. v_rms is v. The relationship between the two is 3*v_x^2 = v_rms^2. This is because v_x^2+v_y^2+v_z^2=3*v_x^2=v^2.
  4. Apr 30, 2008 #3
    Ooooh yeeeeeaaah.

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