How does diffusion create equilibrium

Imagine a cup of water. You drop some blue ink in it. What happens next is the blue ink spreads out in the water. This is diffusion. It happens because there's a concentration gradient. The blue ink particles will move and flow to the region with less blue ink particles. When all the ink is spread and the cup of water all turns blue, this is where we all equilibrium. All sides are same, same concentration. Note that blue ink particles still move in the blue water, but the rate of the left side moving to right and the right side moving to left is the same, so you don't see one side being darker or lighter.

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