This guide covers IGCSE Chemistry topic 7: chemical reactions. You will revise types of reaction (combination, decomposition, displacement, precipitation, neutralisation), rate of reaction (factors, collision theory), and reversible reactions (equilibrium).

Key concepts to revise

• Types – Combination (A + B → C); decomposition (C → A + B); displacement (A + BC → AC + B); precipitation (insoluble solid forms); neutralisation (acid + base → salt + water).
• Rate – Affected by concentration, temperature, surface area, catalyst; collision theory (more collisions, more frequent successful collisions).
• Reversible – Reaction can go both ways (e.g. N2 + 3H2 ⇌ 2NH3); equilibrium when forward and backward rates equal.
• Catalyst – Speeds up reaction; not used up; lowers activation energy.

Exam tips and command words

• State – The type of reaction from an equation (e.g. displacement, neutralisation).
• Describe – How to measure rate (e.g. loss of mass, volume of gas, time for cross to disappear).
• Explain – Why rate increases when concentration or temperature increases (more collisions; more successful collisions).
• Explain – What happens at equilibrium (forward and backward rates equal; concentrations constant).

Common mistakes

• Saying a catalyst “takes part in the reaction” (it is not used up; it is recovered).
• Confusing rate (speed of reaction) with yield (amount of product).
• Saying at equilibrium “reaction stops” (reaction continues both ways; rates are equal).

Revision checklist

• Identify the type of reaction from a given equation (combination, decomposition, displacement, neutralisation).
• Describe how to measure the rate of a reaction (one method).
• Explain the effect of concentration, temperature and catalyst on rate (collision theory).
• Describe reversible reactions and equilibrium (rates equal; concentrations constant).

Next steps

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