Philip-flop
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I'm having trouble working through the following example. Can someone please explain this to me...

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kkboyk
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(Original post by Philip-flop)
I'm having trouble working through the following example. Can someone please explain this to me...

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They have basically just used the equation for Fick's Law and subbed in all the values:

Rate of diffusion = (area of diffusion x difference in concentration ) / (thickness of surface over which diffusion occurs)
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drinktheoceans
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Fick's Law basically takes into account what affects diffusion.

A larger surface area for diffusion to take place upon, increases the rate of diffusion as the likelihood of collisions taking place increase. A larger concentration gradient (difference in concentration) also increases the rate of diffusion as molecules move from an area of high concentration to an area of low concentration. That is why they are numerators in the equation.

However a thicker surface would increase the barrier to diffusion, and so the larger the thickness of the surface, the smaller your rate of diffusion. As a larger value of surface thickness would decrease the rate of diffusion, it is a denominator in the equation.
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Philip-flop
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(Original post by kkboyk)
They have basically just used the equation for Fick's Law and subbed in all the values:

Rate of diffusion = (area of diffusion x difference in concentration ) / (thickness of surface over which diffusion occurs)
Yeah I know how to use the simplified version of Fick's Law but will I have to know how to use the formula that's in the example? Because I really don't know how to work it out.
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AortaStudyMore
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(Original post by Philip-flop)
Yeah I know how to use the simplified version of Fick's Law but will I have to know how to use the formula that's in the example? Because I really don't know how to work it out.
That is the simplified version lol, the only thing in that equation you might not have come across is the permeability constant, but that just takes into account varying permeability of membranes
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kkboyk
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(Original post by Philip-flop)
Yeah I know how to use the simplified version of Fick's Law but will I have to know how to use the formula that's in the example? Because I really don't know how to work it out.
Every value you will need is given in that mini paragraph: the concentration difference is already given ( C1 = 2.3 x 10^(-16) mol um^(-3) and C2 = 9.0 x 10^(-17) mol um , so the difference is C1 - C2)

The area of diffusion is also given which is 2.2, so times it by the permeability constant (which will be different for each organism). The last bit which is the thickness of the surface is 1. That is all you literally need to do.
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Philip-flop
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(Original post by kkboyk)
Every value you will need is given in that mini paragraph: the concentration difference is already given ( C1 = 2.3 x 10^(-16) mol um^(-3) and C2 = 9.0 x 10^(-17) mol um , so the difference is C1 - C2)

The area of diffusion is also given which is 2.2, so times it by the permeability constant (which will be different for each organism). The last bit which is the thickness of the surface is 1. That is all you literally need to do.
Thank you! I know how to substitute the values into the formula but don't know how to type any of it into a calculator. So I'm still having trouble getting the answer as: 3.7 x 10^(-18) mol um^(-2) s^(-1)
Sorry if I'm being stupid
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