What do the units of diffusion coefficient mean?

In summary, the diffusion coefficient, D, has units of cm^2/s and represents the speed per gradient of density. This is similar to the units for speed, which is a certain length traveled in a certain time. Fick's law states that flux is equal to the diffusion coefficient multiplied by the gradient of density. Therefore, doubling the coefficient will result in either twice the speed or the same speed with only half the gradient of density. However, understanding the intuition behind these units may be difficult.
  • #1
kop442000
34
0
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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  • #2
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:
 

Related to What do the units of diffusion coefficient mean?

1. What are the units of diffusion coefficient?

The units of diffusion coefficient depend on the system of measurement being used. In the International System of Units (SI), the units are meters squared per second (m^2/s). In the cgs system, the units are centimeters squared per second (cm^2/s).

2. How is diffusion coefficient measured?

Diffusion coefficient can be measured experimentally using techniques such as diffusion-weighted magnetic resonance imaging (DW-MRI) or Brownian motion analysis. It can also be calculated using theoretical models based on the properties of the diffusing particles and the environment they are in.

3. What is the significance of diffusion coefficient units?

The diffusion coefficient units are important because they provide a measure of how quickly particles diffuse in a given system. They also allow for comparisons between different systems and can be used to study the properties of the diffusing particles.

4. How does temperature affect diffusion coefficient units?

As temperature increases, diffusion coefficient typically increases as well. This is because higher temperatures lead to an increase in the kinetic energy of particles, making them move more quickly and thus diffuse faster. The relationship between temperature and diffusion coefficient can be described by the Arrhenius equation.

5. Can diffusion coefficient units be converted between different systems of measurement?

Yes, diffusion coefficient units can be converted between different systems of measurement. For example, to convert from SI units (m^2/s) to cgs units (cm^2/s), you can multiply by a conversion factor of 10^4. It is important to note that the numerical value of the diffusion coefficient may also change when converting between systems due to differences in the units themselves.

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