What is Diffusion?
[[File:Diffusion.svg|thumb|right|200px|A diagram of diffusion happening. The first diagram shows particles in a liquid. The second shows the same liquid a few seconds later after the particles have spread out]] '''Diffusion''' is a process where [[molecule]]s of a material move from an area of high [[wikt:concentration|concentration]] (where there are many molecules) to an area of low concentration (where there are fewer molecules)<ref>{{Cite web|url = http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/cells/cells3.shtml|title = BBC - GCSE Bitesize: Diffusion}}</ref>until it has reached [[equilibrium]] (molecules evenly spread). Diffusion usually happens in a mixture in [[gas]], a [[liquid]] and occasionally [[Colloid|colloids]]. It is possible to see diffusion happening when two liquids are mixed in a [[wikt:transparent|transparent]] container. It describes the constant movement of particles in all liquids, gases and colloids. These particles move in all directions bumping into each other. == Examples == * A [[sugar]] cube is left in a beaker of water for a while. * The smell of [[ammonia]] spreads from the front of the classroom to the back of the room. * Fumes of perfume rise from the bottle when the top is removed. * Food coloring dropped on the beaker spreads out. * the smell of food spread in the whole house [[Molecules]] tend to move from places of high concentration to places of low concentration, just by moving randomly. For example, there is more [[oxygen]] in a [[lung]] than there is oxygen in the [[blood]] so oxygen molecules will tend to move into the blood. Similarly, there is more [[carbon dioxide]] molecules in the blood than in the lung so carbon dioxide molecules will tend to move into the lung. It happens in [[cell biology]], where small molecules simply diffuse through the [[cell membrane]], but larger molecules only get through by using energy: see [[active transport]]. The random movement of fluid molecules makes them spread out until a boundary stops them. Diffus