Understanding Diffusion: Mean Free Path, Random Walk, and Fick's Law, Slides of Physics

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Diffusion

Atomic Collision 

Molecules in a gas make collisions with each other aswell as the wall.



There is an average time and average distancebetween collisions.

Random Walk



A molecule will move inrandom directions after eachcollision. 

If it starts in one place it willeventually move away. 

The motion is called arandom walk.

Concentrated Region 

Molecules in a concentratedregion will disperse into therest of the medium. 

The difference inconcentrations is theconcentration gradient.

C x

C

C x

2

1

C

1

 x

C

2

Fick’s Law 

The rate of diffusion depends on the concentrationgradient, area, and diffusion constant.



J

measures mol/m



There is a diffusion time

t

for diffusion in one direction

over a distance

x

C t

C

DA

J^

2

1

x^ D

t^

2