Frequently Examined
Endothermic reactions are often tested alongside exothermic reactions in compare-and-contrast questions. Key areas:
- Comparing ฮH signs โ positive for endothermic, negative for exothermic
- Drawing/interpreting energy profiles โ products higher for endothermic
- Reversible reactions โ if forward is endothermic, reverse is exothermic
- Photosynthesis and thermal decomposition โ most commonly cited examples
- Identifying from experimental data โ temperature DROPS โ endothermic
Edexcel 1CH0: Examined in Paper 2 (1CH0/2). Edexcel tests the difference between exothermic and endothermic reactions using temperature change data. In Edexcel-style questions, the command word "Suggest" appears frequently โ use your chemistry knowledge to apply to an unfamiliar context.
Quick Check: The decomposition of calcium carbonate is endothermic: CaCOโ โ CaO + COโ. What would be the sign of ฮH for the REVERSE reaction (CaO + COโ โ CaCOโ)?
The reverse reaction would be EXOTHERMIC, so ฮH would be NEGATIVE. When a reaction is reversed, the energy change is equal in magnitude but opposite in sign. If the forward reaction absorbs energy (+ฮH), the reverse reaction releases the same amount of energy (โฮH).
This exam focus covers Exam Focus 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 10 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.