Unit Overview
Chemical Reactions
CIE IGCSE Chemistry· 5 min read 📊 12-15% of total exam marks across MCQ and structured sections
1. Unit at a glance
You will start by learning to measure reaction rates and apply collision theory to explain how temperature, concentration, surface area, and catalysts change reaction speed. Next, you will explore reversible reactions and dynamic equilibrium, including how external changes shift equilibrium position in industrial applications. You will finish by mastering redox classification, a core reaction type critical to corrosion, energy production, and biological systems.
Work through the following sub-topics in order to build a complete understanding of this unit:
Rate of Reaction
Learn to calculate reaction rates and explain how key variables change reaction speed using collision theory.
★★⏱ 10 min
Reversible Reactions and Equilibrium
Explore dynamic equilibrium, Le Chatelier’s Principle, and applications to high-yield industrial chemical production.
★★★⏱ 12 min
Redox
Identify redox reactions using three complementary classification systems: electron transfer, oxidation state changes, and oxygen/hydrogen gain/loss.
★★★⏱ 11 min
2. Common Pitfalls
Wrong move:
Confusing dynamic equilibrium with reaction completion
Why:
At equilibrium, forward and reverse reaction rates are equal, not zero, so reactant and product concentrations stay constant but reactions are still active.
Correct move:
Always link equilibrium to equal forward/reverse reaction rates, not zero reaction activity.
Wrong move:
Using total product volume to compare reaction rates
Why:
Reaction rate measures change in reactant/product per unit time, not total amount produced over the full reaction.
Correct move:
Divide changes in mass, volume, or concentration by time elapsed to calculate valid reaction rates.
Wrong move:
Assuming only metals undergo oxidation/reduction
Why:
Non-metals including chlorine, sulfur, and nitrogen regularly change oxidation states in common reactions.
Correct move:
Calculate oxidation states for all elements in a reaction to accurately identify oxidizing and reducing agents.
3. Quick Reference Cheatsheet
Key Concept/Formula | Definition/Unit | Related Sub-topic |
|---|---|---|
Rate of reaction | Rate of Reaction | |
Collision theory requirement | Particles must collide with minimum activation energy and correct orientation to react | Rate of Reaction |
Dynamic equilibrium conditions | Closed system, equal forward/reverse reaction rates, constant species concentrations | Reversible Reactions and Equilibrium |
Le Chatelier’s Principle | Equilibrium systems shift to oppose external changes to concentration, temperature, or pressure | Reversible Reactions and Equilibrium |
Oxidation (electron transfer definition) | Loss of electrons | Redox |
Reduction (oxidation state definition) | Decrease in oxidation number | Redox |
Catalyst effect on equilibrium | Speeds up rate of reaching equilibrium, no change to final equilibrium position | Reversible Reactions and Equilibrium |
What's Next
Begin your study of this unit with the Rate of Reaction sub-topic, where you will practice calculating rates from experimental data and apply collision theory to explain real-world reaction speed changes. Once you have worked through all three sub-topics in this unit, you will be ready to progress to the next unit on Acids, Bases and Salts, which builds directly on reaction principle knowledge from this section.