Diffusion

Diffusion is the movement of particles from a high concentration to a low concentration. Diffusion can be seen as a spreading out of particles resulting in an even distribution of the particles. You can see diffusion when you place a drop of food colouring in water. The colour slowly spreads out through the water. If matter were not made of particles that are constantly moving then we would only see a clump of colour when we put the food colouring in water, as there would be nothing that could move about and mix in with the water. *Diffusion occurs in solids too. 

Diffusion is a result of the constant thermal motion of particles. In 1828 Robert Brown observed that pollen grains suspended in water moved about in a rapid, irregular motion. This motion has since become known as Brownian motion. Brownian motion is essentially diffusion of many particles. Brownian motion can also be seen as the random to and fro movement of particles.

The rate of diffusion is dependent on:

1. Temperature

2. Molecular Mass of the particles

3. Concentration gradient

From the kinetic particle Theory, it can be deduced that the rate of diffusion depends on the speed of the particles. The faster the particles move, the higher the rate of diffusion.

Hence, the higher the temperature, the higher the rate of diffusion.

Under the same conditions of temperature and pressure, a substance with a lower relative Molecular Mass diffuses faster than a substance with a higher Molecular Mass. Hence,the lower the Molecular Mass, the higher the rate of diffusion.

The following video will show how temperature and MW affects the rate of diffusion.