Note:

Cambridge IGCSE Chemistry Notes on Chemical Energetics 2026/2027/2028

Syllabus Content:

 Exothermic and endothermic reactions

Core

1. State that an exothermic reaction transfers thermal energy to the surroundings leading to an increase in the temperature of the surroundings
2. State that an endothermic reaction takes in thermal energy from the surroundings leading to a decrease in the temperature of the surroundings
3. Interpret reaction pathway diagrams showing exothermic and endothermic reactions

Supplement

1. State that the transfer of thermal energy during a reaction is called the enthalpy change, ∆H, of the reaction. ∆H is negative for exothermic reactions and positive for endothermic reactions 
2. Define activation energy, Ea, as the minimum energy that colliding particles must have to react 
3. Draw and label reaction pathway diagrams for exothermic and endothermic reactions using information provided, to include: (a) reactants (b) products (c) enthalpy change of the reaction, ∆H (d) activation energy, Ea
4. State that bond breaking is an endothermic process and bond making is an exothermic process and explain the enthalpy change of a reaction in terms of bond breaking and bond making
5. Calculate the enthalpy change of a reaction using bond energies