What is it
This topic extends KS3's exothermic/endothermic distinction with reaction profile diagrams, activation energy, calculating energy changes from bond energies, and how simple cells and batteries produce electricity from chemical reactions.
Why it matters
Bond-energy calculations are one of the more mathematically demanding parts of GCSE chemistry and a reliable source of higher-tier marks for well-prepared students.
Exam tip
Remember the rule: energy change = energy to break bonds (reactants) − energy released forming bonds (products) — get the subtraction order right, since a reversed answer gives the wrong sign for the reaction type.
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