2 g of green coloured crystals of ferrous sulphate are heated in a dry boiling tube. Name the type of chemical reaction taking place. Write the balanced chemical equation for the reaction. Is this an exothermic or an endothermic reaction ?
Generated by claude-sonnet-4-6 · 2026-06-14 10:31 · grounding rag
Model Answer
Type of reaction: Decomposition reaction (thermal decomposition)
Balanced chemical equation:
$$2\text{FeSO}_4(s) \xrightarrow{\Delta} \text{Fe}_2\text{O}_3(s) + \text{SO}_2(g) + \text{SO}_3(g)$$
Ferrous sulphate (green) decomposes on heating to form ferric oxide (reddish-brown), sulphur dioxide and sulphur trioxide gases.
Exothermic or Endothermic: This is an endothermic reaction because energy (heat) is absorbed to break down the reactant into simpler products.
Source: Chapter 1, Section 1.2.2 – Decomposition Reaction
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Explanation
- 1 mark for naming the reaction type (thermal decomposition).
- 1 mark for the correct balanced equation with state symbols.
- 1 mark for correctly identifying it as endothermic with the reason (energy is absorbed).
- Examiners expect you to state why it is endothermic — decomposition reactions require energy input, so they are endothermic.
- Don't forget: the green colour changes to reddish-brown (Fe₂O₃); mentioning this shows observation-based understanding, though not strictly required for marks here.