Decomposition reactions are described as endothermic. What does the term 'endothermic' mean? Explain why decomposition reactions require an external supply of energy to proceed.
Generated by claude-sonnet-4-6 · 2026-06-26 00:54 · grounding rag
Model Answer
Endothermic means a reaction in which energy is absorbed from the surroundings.
In decomposition reactions, a single substance breaks down into two or more substances. Breaking the chemical bonds in the reactant requires energy. Since energy must be supplied (as heat, light, or electricity) to break these bonds, decomposition reactions are endothermic.
Source: Chemical Reactions and Equations, Chapter 1 — What you have learnt
Explanation
- 1 mark for correctly defining endothermic (energy is absorbed).
- 1 mark for explaining that bond-breaking in the reactant requires an external energy input, linking it specifically to decomposition reactions.
- Examiners expect you to contrast with exothermic (energy released) implicitly by using precise language like "absorbed."
- Avoid vague phrases like "needs energy to work" — say bonds must be broken and energy is absorbed from surroundings.