How does doubling the temperature affect diffusion rate?

D ∝ √T, so doubling T increases D by √2 ≈ 1.41.

At equilibrium, do particles stop moving? Why?

Particles continue moving randomly but net flux = 0.

Why does a larger pore size increase diffusion flux proportionally but larger molecules diffuse more slowly?

Pore size sets the cross-sectional area; molecular mass affects D via √(1/m).

Pro 🔒~20 min

Diffusion

Watch particles spread from high to low concentration

How it works

Diffusion is the net movement of particles from regions of high concentration to low concentration driven by thermal motion. Fick's First Law states that the diffusion flux J is proportional to the concentration gradient. Higher temperatures increase particle kinetic energy, speeding diffusion. Membrane pore size selectively restricts passage — larger molecules diffuse more slowly through smaller pores.

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Step-by-step

The simulation starts with high concentration on the left and low on the right.
Watch particles drift across the membrane.
Increase temperature to speed up diffusion.
Change pore size to limit which particles cross.
Plot concentration vs. time to see exponential equilibration.

Key formulas

$J = -D\frac{\Delta C}{\Delta x}$ Fick's First Law of Diffusion
$D \propto \sqrt{\frac{k_B T}{m}}$ Diffusion coefficient vs. temperature

Frequently asked questions

How does doubling the temperature affect diffusion rate?: D ∝ √T, so doubling T increases D by √2 ≈ 1.41.
At equilibrium, do particles stop moving? Why?: Particles continue moving randomly but net flux = 0.
Why does a larger pore size increase diffusion flux proportionally but larger molecules diffuse more slowly?: Pore size sets the cross-sectional area; molecular mass affects D via √(1/m).