Edexcel IGCSE Chemistry · Section 3
Physical Chemistry
Energetics, energy level diagrams, rates of reaction, catalysts, reversible reactions and equilibrium.
What this section covers
This section explains how fast reactions happen and how energy changes during reactions. Students revise exothermic and endothermic reactions, rates, catalysts and equilibrium.
- Interpret exothermic and endothermic reactions using energy level diagrams.
- Explain the factors that affect rates of reaction using collision theory.
- Understand catalysts, reversible reactions and dynamic equilibrium.
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1
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Exothermic & Endothermic Reactions; Calorimetry
Spec 3.1-3.4
Exothermic and endothermic reactions, and measuring temperature change by calorimetry.
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2
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Calorimetry and Molar Enthalpy Calculations
Spec 3.2-3.4, 3.8
Covers collect reliable calorimetry data, Calculate Q using mc delta T and Calculate molar enthalpy change with the correct sign.
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3
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Energy Level Diagrams & Bond Energies
Spec 3.5C-3.7C
Energy level diagrams and calculating energy changes from bond energies.
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4
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Bond-Energy Calculations and Reversible Heating (Paper 2)
Spec 3.7C, 3.18
Covers calculate enthalpy change from bond energies, Interpret the sign of the answer and Explain heating ammonium chloride.
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5
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Energy Changes (Required Practical)
Spec 3.8
Required practical: investigating the temperature changes of reactions.
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6
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Rates of Reaction Required Practicals
Spec 3.9, 3.15-3.16
Covers plan fair tests for rate factors, Compare marble-chip surface areas and Investigate catalysts for hydrogen peroxide decomposition.
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7
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Rates of Reaction: Factors & Collision Theory
Spec 3.9-3.11
The factors that affect rate of reaction, explained by collision theory.
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8
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Catalysts & Reaction Profiles
Spec 3.12-3.14C
How catalysts speed up reactions, shown on reaction profile diagrams.
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9
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Investigating Rates of Reaction
Spec 3.15-3.16
Required practical: investigating how conditions affect the rate of a reaction.
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10
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Reversible Reactions
Spec 3.17-3.18
Reversible reactions and how they can reach a balance.
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11
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Dynamic Equilibrium & Le Chatelier's Principle
Spec 3.19C-3.22C
Dynamic equilibrium and how Le Chatelier's principle predicts the effect of changing conditions.
Frequently asked questions
What is the difference between exothermic and endothermic reactions?
Exothermic reactions release energy and warm the surroundings; endothermic reactions take in energy and cool the surroundings.
What factors affect the rate of a reaction?
Temperature, concentration (or pressure for gases), surface area and catalysts — all explained by collision theory.
How do catalysts speed up reactions?
A catalyst provides a different pathway with a lower activation energy, without being used up in the reaction.
What is Le Chatelier's principle?
If you change the conditions of a reaction at equilibrium, the position of equilibrium shifts to oppose that change.
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