In endothermic reactions, energy is transferred FROM the surroundings INTO the reacting chemicals. This causes the temperature of the surroundings to decrease.
Energy in Products > Energy in Reactants
Energy is absorbed from surroundings to make up the difference
Common examples of endothermic reactions:
- Photosynthesis — plants absorb light energy to make glucose
- Thermal decomposition — breaking down compounds using heat (e.g., CaCO₃ → CaO + CO₂)
- Dissolving ammonium nitrate — used in sports injury cold packs
- Citric acid + sodium hydrogencarbonate — sherbet reaction
- Electrolysis — requires continuous energy input
This deep dive covers Deep Dive: Where Does the Energy Come From? within Endothermic Reactions for GCSE Chemistry. Revise Endothermic Reactions in Energy Changes for GCSE Chemistry with 20 exam-style questions and 14 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 4 of 12 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Endothermic Reactions
In an endothermic reaction, energy is:
Explain why a sports cold pack becomes cold when activated.