Principles of Chemistry · 0 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 6% of your exam marks.
Appears regularly as short-answer questions on particle diagrams and state changes.
Recognise and explain diffusion
What comes up: you name the process by which particles spread and mix (the answer is diffusion), or explain why a coloured gas or solution spreads out evenly.
Write: diffusion is the spreading of particles from where they are more concentrated to where they are less concentrated, because the particles are in constant random motion. It is faster in gases (particles move faster and are further apart) and faster when hotter.
Watch out: don't confuse it with dilution (adding more solvent) — that's the classic wrong answer the mark scheme rejects. Diffusion needs no stirring and no energy input, and still happens even when the gas is denser than the air.