Diffusion

Particles in a liquid and a gas move continuously. Because of this movement, particles will spread themselves evenly throughout a liquid or a gas.

If there is a situation where particles of a substance are in a higher , they will therefore move from this region to where they are in a lower concentration. This is called .

It is important to remember that the particles:

will move in both directions, but there will be a movement from high to low concentration
will end up evenly spread throughout the liquid or gas but will continue to move

Diffusion of coloured chemicals

If a crystal of a coloured chemical, eg potassium manganate(VII), is placed in water, the particles spread out and mix with the water particles. The process is:

the potassium manganate(VII) has dissolved
the potassium manganate(VII) is the
the water is the
the mixture that results is the

The particles have moved from a region of high concentration in the crystal to a low concentration in the water. This difference in concentration is called a . Particles will move down a concentration gradient, from a high concentration to a low concentration.

As well as diffusion occurring between different regions, it also occurs across , between the outside and inside of cells.