• Support PF! Buy your school textbooks, materials and every day products Here!

Molecular diffusion question; fick's first law

  • Chemistry
  • Thread starter aquabum619
  • Start date
  • #1
29
0

Homework Statement


Calculate the flux of oxygen across a square centimeter membrane [2[tex]\mu[/tex], or 2x10 [tex]^{-6}[/tex]m thick if the concentration on the right hand side of the membrane is 4mL/L and on the left side is 2mL/L.

Homework 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

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[tex]\mu[/tex], which resulted in a flux of 1x10[tex]^{6}[/tex]... 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[tex]^{-5}[/tex]x[4mL/L - 2mL/L]= 6x10[tex]^{-5}[/tex]. 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!
 
Last edited:

Answers and Replies

  • #2
Mapes
Science Advisor
Homework Helper
Gold Member
2,593
20
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.
 
  • #3
29
0
after doing a little research, I come to realize that the diffusion equation (Fick's first law) is actually

Flux = -D[([tex]\Delta[/tex]C)/([tex]\Delta[/tex]x]
where D is the diffusion coefficient;
where C is the concentration
where [tex]\Delta[/tex]x is the thickness of the membrane

therefore, -3x10^-5 [(2mL/L)/(2x10^-6m)]= -30 [mol]/[m^2 sec]
 
Last edited:

Related Threads on Molecular diffusion question; fick's first law

  • Last Post
Replies
3
Views
5K
  • Last Post
Replies
4
Views
4K
Replies
0
Views
3K
Replies
1
Views
4K
Replies
1
Views
947
Replies
2
Views
2K
Replies
1
Views
1K
Replies
6
Views
6K
Top