๐ฏ Common Question Types:
- "Explain why this reaction is endothermic" (2 marks)
- "Draw an energy profile for an endothermic reaction" (2 marks)
- "The forward reaction is endothermic โ what can you say about the reverse?" (1-2 marks)
- "Is photosynthesis exothermic or endothermic? Explain." (2 marks)
๐ Key Command Words:
- Explain โ state the energy direction (from surroundings to chemicals) and the effect (temperature falls)
- Draw โ label axes, show products ABOVE reactants, include activation energy peak
- Suggest โ use your knowledge to propose an explanation for unfamiliar data
โ ๏ธ Common Mistakes to Avoid:
- Drawing the energy profile with products BELOW reactants (that's exothermic!)
- Using negative ฮH for endothermic โ endothermic ฮH is always POSITIVE
- Saying "endothermic means no energy is released" โ energy is both absorbed AND released in every reaction; endothermic means more is absorbed than released overall
- Forgetting that photosynthesis is the most important endothermic reaction to know
Quick Check: Give TWO examples of endothermic reactions and explain how you know they are endothermic.
1. Photosynthesis โ plants absorb light energy from the sun to convert COโ and water into glucose. Energy is taken IN from the surroundings (sunlight), so it is endothermic. 2. Thermal decomposition of calcium carbonate โ CaCOโ โ CaO + COโ. Continuous heating is required to make this reaction happen, meaning energy must be continuously absorbed from the surroundings. ฮH is positive for both reactions.
This exam tips covers Exam Tips for Endothermic Reactions 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 11 of 12 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Practice questions for Endothermic Reactions
In an endothermic reaction, energy is:
Explain why a sports cold pack becomes cold when activated.