also known as random motion, this is the spontaneous and unpredictable movement of particles or objects that results from their thermal energy

the process by which particles or substances spread from areas of higher concentration to areas of lower concentration; it occurs as a result of random thermal motion of particles, and it is driven by the difference in concentration between two regions

the amount of a substance present in a given volume or weight of a mixture or solution

the difference in concentration between a region of a solution or gas that has a high concentration of particles and a region that has a relatively lower concentration of particles

when two molecules bump into each other