What is happening?
Particles move randomly, but a crowded region has more particles available to cross into a less crowded region. The net flow follows the concentration gradient until both sides become similar.
HEAT & THERMODYNAMICS · INTERACTIVE LAB 50
Diffusion simulation
Watch random molecular motion erase a concentration gradient. Compare two substances, open a membrane and track the approach to dynamic equilibrium.
Left concentration—
Right concentration—
Difference—
Mixed0%
Time0.0 s
Dynamic equilibrium
At equilibrium the particles do not stop. They continue crossing in both directions at approximately equal rates, so the large-scale concentration remains stable.
Fick’s law
The diffusive flux is proportional to the negative concentration gradient: J = −D∇C. Higher temperature is represented here by faster random motion and quicker mixing.
Model note: This is a simplified two-dimensional random-walk model for education. It illustrates diffusion trends, not a full molecular-dynamics calculation.