Diffusion occurs due to the thermal displacement of atoms or molecules, which cause these particles to randomly move in various media, such as solids, liquids or gases. Generally, atoms or molecules diffuse from an area of higher concentration to an area of lower concentration until a substance is of uniform concentration.
Diffusion is a type of passive transport, which is classified into three main categories: simple, facilitated and channel diffusion. The rate at which diffusion takes place is affected by several factors. These include particle size, concentration gradient, particle solubility, distance traveled by the particle, temperature and surface area across which the particle can move. Diffusion does not occur when a substance is at zero degrees Kelvin.