-Describe and explain diffusion in terms of kinetic particle theory

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. 

Example:  In liquids: potassium manganate (VII) in a beaker of water. The purple crystals dissolve, purple colour spreads  and turn water purple. The particles of potassium manganate (VII) diffuse into the water towards regions in the liquid that have lower concentration. Eventually, the concentration of potassium manganate (VII) become the same throughout the liquid. Diffusion stops. 

Liquid bromine evaporates to become vapour. Particles of bromine move upwards into the gas jar on top. Particles of air move downwards. 

After few minutes, both gas jars appeared to have same shade of brown. Particles of air and bromine had spread evenly in the gas jars. Diffusion stops but particles are still constantly moving. 

Diffusion rate is affected by temperture and relative molecular mass. 

Particles have higher kinetic energy ar higher temperature and move more quickly. 

-Describe and explain the effect of relative molecular mass on the rate of diffusion of gases

The lower the relative mass of its particles, the faster a gas will diffuse.
Ammonia solution and hydrochloric acid will evaporate to become ammonia gas and hydrogen chloride respectively.
Colourless gases, ammonia and hydrogen chloride, diffuse down the tube and react to form white solid of ammonium chloride.

The white smoke forms closer to B as the ammonia molecules with lower relative molecular mass of 17 will diffuse faster and move further than the hydrogen chloride molecules with relative molecular mass of 36.5