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Homework Help: Fick's Law of Diffusion

  1. Nov 12, 2011 #1
    Suppose that a tracheae is 1.17 mm long with a cross-sectional area of 1.01 x 10-9m2. The concentration of oxygen in the air outside the insect is 0.659 kg/m3, and the diffusion constant is 1.99 x 10-5 m2/s. If the mass per second of oxygen is diffusing through a trachea is 1.50 x 10-12 kg/s, then find the oxygen concentration at the interior end of the tube.

    m= (DA(deltaC))t / L

    I re-arranged the equation to solve for the change in concentration, (delta)C.
    deltaC = mL / DA. I know the given value for the outside concentration will be moved over to the other side. I think that the concentration given for the outside of the insect would be the same as initial concentration and the concentration I am solving for would be the final concentration but not exactly sure on this. So I added the concentration given to the other side of the equation to isolate the final concentration. I calculated this to be 8.73E8 kg/s, however this is incorrect. Any suggestions?
  2. jcsd
  3. Nov 12, 2011 #2


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    Staff: Mentor

    You lost the 't' when re-arranging.

    Using your formula and data, I make delta C to be 0.0873 kg/m3
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