Diffusion occurs when particles spread. They move from a region where they are in high concentration to a region where they are in low concentration. Diffusion happens when the particles are free to move. This is true in gases and for particles dissolved in solutions - but diffusion does not occur in solids.

Why does diffusion occur?

Diffusion is the process by which particles of one substance spread out through the particles of another substance. ... Diffusion happens on its own when the particles spread out from an area of high concentration , where there are many of them, to areas of low concentration where there are fewer of them.

Why does diffusion occur quizlet?

Diffusion occurs because molecules are always bumping into each other and moving from one to another concentration.