Particles move about randomly, and after a while they end up evenly spaced.
Don't Be Put Off by the Fancy Word.
"Diffusion" is simple. It's the gradual movement of particles from places where there are lots of particles to places where there are fewer. The best example I can come up with is imagine two parties. one party is far to crowded so you leave and go to the less crowded party. But you can't say that in an exam just write this:
"Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration.
Diffusion happens in both liquids and gases - that's because the particles in these substances are free to move about randomly. The simplest type is when different gases diffuse through each other. If I sprayed perfume into a room eventually you would not be able to…