Myers Science Hub Premium • IGCSE Chemistry 0620

C5 Chemical Energetics: Exothermic and Endothermic Reactions

A complete lesson covering thermal energy transfer, reaction pathway diagrams, enthalpy change, activation energy, bond breaking, bond making and bond energy calculations. Responses submit to the backend for teacher manual grading.

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Syllabus Objectives Covered

State that an exothermic reaction transfers thermal energy to the surroundings, increasing the temperature of the surroundings.
State that an endothermic reaction takes in thermal energy from the surroundings, decreasing the temperature of the surroundings.
Interpret reaction pathway diagrams showing exothermic and endothermic reactions.
State that the transfer of thermal energy during a reaction is called the enthalpy change, ΔH.
State that ΔH is negative for exothermic reactions and positive for endothermic reactions.
Define activation energy, E_a, as the minimum energy colliding particles must have to react.
Draw and label reaction pathway diagrams to show reactants, products, ΔH and E_a.
State that bond breaking is endothermic and bond making is exothermic.
Calculate enthalpy change using bond energies.

Chemical Energetics Toolkit

Exothermic
Transfers thermal energy to surroundings. Surroundings get warmer. ΔH is negative.

Endothermic
Takes in thermal energy from surroundings. Surroundings get cooler. ΔH is positive.

Activation energy
Minimum energy needed for colliding particles to react.

Bond breaking
Requires energy. Endothermic process.

Bond making
Releases energy. Exothermic process.

Bond energy calculation
ΔH = energy to break bonds − energy released making bonds.

Reaction Pathway Reminder

Reactants

Products

Energy

Progress of reaction

E_a

ΔH

For exothermic reactions, products are lower in energy than reactants. For endothermic reactions, products are higher in energy than reactants.

Embedded Video Learning Stations

1. Exothermic and endothermic reactions

2. Energy profile diagrams

3. Activation energy

4. Bond breaking and bond making

5. Bond energy calculations

6. Enthalpy change overview

Teachers should preview videos before classroom use.

Guided Notes

1. Explain the difference between exothermic and endothermic reactions.

2. Explain what ΔH means and how its sign changes.

3. Define activation energy.

4. Explain why bond breaking is endothermic and bond making is exothermic.

5. Describe how to calculate ΔH using bond energies.

30-Mark Manual Practice

Answer all parts. Your responses will be sent to the backend sheet for manual marking by your teacher.