What is diffusion?

By definition, diffusion is the movement of particles from a region of high concentration to a region of low concentration. It occurs in liquids and gases where particles can move freely down a concentration gradient.

Have you ever smelt dinner being cooked in the kitchen while you were in another room? As though the smell has wafted in? This is an example of diffusion.

In the kitchen the smell is in high concentration. As it leaves the kitchen it travels down the concentration gradient into another room: a region of low concentration.