The movement of particles in diffusion is determined by a process called random thermal motion. Each particle in a substance has its own individual kinetic energy, which causes it to move randomly and collide with other particles. As a result of these collisions, particles tend to move from areas of higher concentration to areas of lower concentration, as this random motion leads to an overall net movement of particles down the concentration gradient. This random movement is the driving force behind the diffusion process and leads to the spreading out and mixing of particles throughout a medium.
