Energy changes: GCSE Chemistry
Exothermic and endothermic reactions, profiles, bond energies, cells, batteries and fuel cells
The short version
Bond breaking takes energy in; bond making releases energy. Chemical cells use two metals and an electrolyte. Fuel cells use a fuel plus oxygen.
Key idea
Energy is transferred, not created
Grade 2–3: Hand warmers get hot (exo). Ice packs for a sprain get cold (endo).
Grade 5–6: I can define both using the surroundings and I can list the RP steps.
Grade 9: I never say endothermic means no energy involved. Heat loss makes an exothermic temperature rise too small — lid, insulation, stir, repeat, same volume.
Go a bit deeper
ΔH is the gap between reactant and product lines, not the height of the peak
Grade 2–3: You still need a spark to start a fire even if the fire then gives out heat.
Grade 5–6: Exothermic: products lower, arrow down for ΔH. Endothermic: products higher, arrow up.
Grade 9: I never draw the product line at the peak. I say lower activation energy — not gives the particles more energy.
Worked example
Worked example
Grade 2–3: Hand warmers get hot (exo). Ice packs for a sprain get cold (endo). Grade 5–6: I can define both using the surroundings and I can list the RP steps. Grade 9: I never say endothermic means no energy involved. Heat loss makes an exothermic temperature rise too small — lid, insulation, stir, repeat, same volume.
Lessons in this topic
- Exothermic and endothermic reactions
- Reaction profiles
- Bond energies (Higher)
- Cells and batteries (Combined)
- Fuel cells (Higher mention)
- Energy changes recap and profiles practice
In the app each lesson is video (when we have a real YouTube id) then intro, learn and summary steps.
What the examiner wants
ΔH is negative for exothermic. For Higher, energy change = energy to break bonds − energy released making bonds. Hydrogen fuel cells produce water.
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
An exothermic reaction
Ammonium nitrate dissolving and cooling the tube is
Activation energy is
On an exothermic profile, products are
Common mistakes
- The system can get colder while the reaction needs heat. Endothermic does not mean no energy involved. Do not say energy is created.
- Do not draw the product line at the same height as the peak. The peak is the activated state, not the product. Missing labels lose easy marks.
- Using 2HCl as one H–Cl bond is a classic error. Two molecules means two H–Cl bonds. Bond breaking is always endothermic.
- A dead cell is not out of electrons. The reactants have been used up. Two identical metals will not give a useful voltage.
Answers and working
Frequently asked questions
Is GCSE Energy changes on Combined Science and Triple?
Energy changes is on Combined Science and on Triple Chemistry. Progress is shared in the ReviseEasy app.
Which exam board is this Energy changes page for?
The ideas are board-agnostic for AQA, Edexcel, OCR, WJEC and CCEA. Paper lengths and question numbers differ — check your specification.
Is Energy changes Foundation or Higher?
The core ideas appear on both tiers. Higher papers add extra application and some HT-only detail, marked in lessons with a Higher badge.
Learn, try, get feedback, fix the mistake
Open the stepped lesson, then the quiz with hints. Required-practical and calculation questions use the same method you will need in the paper.
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