What do the units of diffusion coefficient mean?

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SUMMARY

The diffusion coefficient (D) is quantified in units of cm²/s, representing the rate at which particles diffuse through a medium. This measurement can be understood through Fick's law, where flux is defined as the product of speed and density. Specifically, the diffusion coefficient indicates how speed varies with the density gradient, expressed as L²/T. Doubling the diffusion coefficient results in either a doubling of the speed or maintaining the same speed with a reduced density gradient.

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kop442000
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I see that the diffusion coefficient (of diffusivity) D has units of something like cm^2 / s. I'm having trouble understanding what those units mean.

For example, speed has such units because something travels a certain LENGTH in a certain TIME.

Could someone explain this for me?

Thank you.
 
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hi kop442000! :smile:

flux is speed times density,

so Fick's law is essentially:

flux = speed times density = diffusion coefficient times the gradient of density

so the diffusion coefficient is speed per gradient ie L/T per 1/L ie L2/T

so if you double the coefficient, you will either double the speed, or you will get the same speed for only half the gradient of density​

sorry, but it doesn't come any more intuitive than that :redface:
 

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