This guide covers IGCSE Chemistry rate of reaction. You will revise how to measure rate (volume of gas; loss of mass; time for cross to disappear; titration), factors (concentration, temperature, surface area, catalyst), collision theory (particles must collide with enough energy; activation energy), and graphs (rate from gradient).

Key concepts to revise

• Rate – Change in amount of reactant or product per unit time; steeper gradient = faster rate; units e.g. cm3/s, g/s.
• Factors – Higher concentration/pressure: more particles per unit volume; more collisions. Higher temperature: particles move faster; more collisions; more have energy ≥ activation energy. Larger surface area: more particles exposed; more collisions. Catalyst: provides alternative pathway; lower activation energy; not used up.
• Collision theory – Reaction when particles collide with sufficient (activation) energy and correct orientation; increasing collisions or energy increases rate.
• Catalyst – Speeds up reaction; not used up; lowers activation energy; shown in energy profile as lower “peak”.

Exam tips and command words

• Describe – How to measure the rate of a given reaction (e.g. volume of gas collected over time; loss of mass).
• Explain – Why rate increases when concentration or temperature increases (collision theory: more collisions; more successful collisions).
• Draw – A graph of amount of product vs time; state how rate changes (gradient); compare two conditions (e.g. with/without catalyst).
• State – The effect of a catalyst (speeds up; not used up; lowers activation energy).

Common mistakes

• Confusing rate (speed; gradient) with yield (total amount of product; final value).
• Saying catalyst “takes part in the reaction” or “is used up” (catalyst is not used up).
• Not linking temperature to activation energy (more particles have E ≥ Ea; more successful collisions).

Revision checklist

• Describe one method of measuring the rate of a reaction (e.g. gas volume; mass loss).
• Explain the effect of concentration, temperature and catalyst on rate (collision theory).
• Draw and interpret a graph of product vs time; state how to find initial rate (gradient at t=0).
• State what a catalyst does and that it is not used up.

Next steps

Book a free trial with an IGCSE Chemistry tutor to practise rate of reaction questions, or explore Tutopiya’s learning portal for more revision resources.