Defining Diffusion
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. This movement occurs due to the random motion of individual particles, leading to a uniform distribution over time. It is a passive process, meaning it does not require an input of external energy.
The Driving Force: Concentration Gradient
The key principle behind diffusion is the concentration gradient—the difference in concentration between two areas. Particles naturally move down this gradient until equilibrium is reached, where the concentration is equal throughout the system. At equilibrium, particles continue to move randomly, but there is no net change in concentration.
A Common Example: Scent Spreading
A practical example of diffusion is when you spray air freshener in one corner of a room. Initially, the scent molecules are highly concentrated near the spray source. Over time, these molecules randomly move and spread throughout the room, diffusing into areas where their concentration is lower until the scent is evenly distributed, or at least perceptible across the room.
Importance in Biological and Chemical Systems
Diffusion is vital across many scientific disciplines. In biology, it's how oxygen moves from the lungs into the bloodstream, how nutrients enter cells, and how waste products exit. In chemistry, it's fundamental to mixing solutions and understanding reaction rates, as reactants must diffuse to come into contact.