Knowledge Organiser: Bond Energies
This topic summary covers Knowledge Organiser: Bond Energies within Bond Energies (HT) for GCSE Chemistry. Revise Bond Energies (HT) in Energy Changes for GCSE Chemistry with 20 exam-style questions and 15 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 15 of 15 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 15 of 15
Practice
20 questions
Recall
15 flashcards
Knowledge Organiser: Bond Energies
Key Terms
- Bond energy — energy to break 1 mol of a bond (kJ/mol)
- ΔH — energy in (breaking) minus energy out (making)
- Breaking bonds — endothermic (requires energy)
- Making bonds — exothermic (releases energy)
Must-Know Facts
- Breaking bonds ALWAYS requires energy (endothermic)
- Making bonds ALWAYS releases energy (exothermic)
- ΔH = Σ(breaking) − Σ(making)
- Negative ΔH → exothermic; Positive ΔH → endothermic
- Double/triple bonds have higher bond energies
- Count ALL bonds × stoichiometric coefficients
Key Equations
- ΔH = Σ(bond energies broken) − Σ(bond energies formed)
- Negative result → exothermic; Positive result → endothermic
- Bond energy units: kJ/mol (energy to break 1 mole of that bond)
Common Mistakes
- Doing the subtraction backwards: ΔH = bonds BROKEN minus bonds FORMED — not the other way round; getting this backwards flips the sign and the answer
- Forgetting to multiply bond energies by coefficients: In CH₄ + 2O₂ → CO₂ + 2H₂O, there are 4 C-H bonds and 2 O=O bonds to break — always count every bond in every molecule
- Saying bond making requires energy: Bond BREAKING requires energy; bond MAKING releases energy — the direction always trips students up
- Using bond energies for ionic compounds: Bond energy calculations only apply to covalent bonds — lattice energy applies to ionic compounds (A-level only)
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Read this section alongside the surrounding pages in Bond Energies (HT). That gives you the full topic sequence instead of a single isolated revision point.
Practice Questions for Bond Energies (HT)
Which statement correctly describes the energy change when chemical bonds are broken?
Explain how you would determine, from a bond energy calculation, whether a reaction is exothermic or endothermic.
Quick Recall Flashcards
20 questions on Bond Energies (HT) — practise free
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