1Diffusion
Particles move randomly, so they spread out from where there are lots of them until they are evenly mixed. This is diffusion.
diffusion
Lesson 2.4 notes
Diffusion and Brownian motion
Particles spread out because they are always moving, and Brownian motion shows us that they are there.
2High to low concentration
Diffusion moves particles from a high concentration (crowded) to a low concentration (less crowded).
concentration
3Faster when warmer
Warmer particles move faster, so diffusion is faster at higher temperatures.
temperature
4Gases, liquids and solids
Diffusion is fast in gases, slow in liquids and almost zero in solids, where the particles can't move around.
random motion
5Brownian motion
A smoke particle jiggles because invisible air particles hit it unevenly from all sides. This is Brownian motion: evidence that particles exist.
Brownian motionevidence
6Diffusion in your body
Oxygen diffuses from the air in your lungs, where there is a lot, into your blood, where there is less.
gas exchange
Explore: Diffusion race
Race purple particles across a gas or a liquid, warm or cold.
Common mistake: Diffusion doesn't need wind or stirring
Particles are always moving randomly. That alone makes them spread out from a high to a low concentration, even in perfectly still air.
Remember
- Diffusion: particles spread from a high concentration to a low concentration.
- It's faster when warmer, fastest in gases and almost zero in solids.
- Brownian motion is evidence that tiny, invisible particles are always moving.
Going further at GCSE