## Molecular diffusion question; fick's first law

1. The problem statement, all variables and given/known data
Calculate the flux of oxygen across a square centimeter membrane [2$$\mu$$, or 2x10 $$^{-6}$$m thick if the concentration on the right hand side of the membrane is 4mL/L and on the left side is 2mL/L.
2. Relevant equations
fick's first law of diffusion
Flux = dC/dx = D[C2-C1] where D is the molecular diffusion constant
molecular diffusion constant for oxygen = 3x10^-5
3. The attempt at a solution

Using the first eq, I took the difference in the concentrations, and divided it by the thickness of the membrane. [4mL/L-2mL/L]/ 2$$\mu$$, which resulted in a flux of 1x10$$^{6}$$... however, the equation did not take into account the molecular diffusion constant of oxygen, which was provided in the problem. So then I tried the second equation. 3x10$$^{-5}$$x[4mL/L - 2mL/L]= 6x10$$^{-5}$$. however, the second equation does not take into account the thickness of the membrane (dx). Im totally lost and have no idea what to do. please help thanks!
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 Recognitions: Gold Member Homework Help Science Advisor You're almost there, but your flux equation looks a little off. Make sure to use the right equation and work through the problem again using the correct units, and things should work out fine.
 after doing a little research, I come to realize that the diffusion equation (Fick's first law) is actually Flux = -D[($$\Delta$$C)/($$\Delta$$x] where D is the diffusion coefficient; where C is the concentration where $$\Delta$$x is the thickness of the membrane therefore, -3x10^-5 [(2mL/L)/(2x10^-6m)]= -30 [mol]/[m^2 sec]

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