Diffusion is really about one thing actually…
which is… that
particles move about randomly!
Spreading out takes time! But start out with particles next to each other, they will be further apart after a while by random movement, and eventually fully spaced apart!
Here is another example
Now think about the following experiment
you see the brown colour of bromine gas spreading to the top after the air in the two cylinders are allowed to mix!
Do you know why the colour of bromine becomes lighter after it has spreaded out?
The reason is because bromine has become LESS CONCENTRATED! 🙂
Next we will look at another example…
which is the very striking purple compound called Potassium Permanganate
Put crystals of Potassium Permanganate at the base of a conical flask and add water… you will see
The reason why this has happened is because
Again, take note that the concentration of Potassium Permanganate particles actually decreased as it spreads out into the liquid! 🙂