This exam focus covers Exam Focus within Bond Energies (HT) for GCSE Chemistry. Revise Bond Energies (HT) in Energy Changes for GCSE Chemistry with 25 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 12 of 15 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
🎯 Exam Focus
Frequently Examined
Bond energy calculations are a Higher Tier topic but appear in many 6-mark questions. Common exam scenarios:
- Calculate ΔH given a balanced equation and bond energy values (show all working)
- Predict exothermic or endothermic from ΔH sign
- Explain in terms of bonds why a reaction is exothermic — must reference which step releases/requires more
- Identify the error in a student's bond energy calculation — check for missing bonds or wrong coefficients
Always show your working — in bond energy calculations, method marks are awarded even if the final answer is wrong.
Edexcel 1CH0: Examined in Paper 2 (1CH0/2). Bond energy calculations to determine whether a reaction is exothermic or endothermic are a standard Higher-tier question type. In Edexcel-style questions, the command word "Suggest" appears frequently — use your chemistry knowledge to apply to an unfamiliar context.
Quick Check: For the reaction N₂ + 3H₂ → 2NH₃, the energy needed to break bonds in the reactants is 2253 kJ/mol and the energy released making bonds in the products is 2346 kJ/mol. Calculate ΔH and state whether the reaction is exothermic or endothermic.
ΔH = energy in − energy out = 2253 − 2346 = −93 kJ/mol. The ΔH is NEGATIVE, so the reaction is EXOTHERMIC. More energy is released making the N-H bonds in ammonia than is needed to break the N≡N bond in nitrogen and the H-H bonds in hydrogen.
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.