When iron reacts with steam, the product is Fe₃O₄, not Fe₂O₃. Write the balanced chemical equation for this reaction and explain why iron cannot be used instead of magnesium in a reaction with cold water to produce hydrogen gas in the laboratory.
Generated by claude-sonnet-4-6 · 2026-06-26 01:05 · grounding rag
Model Answer
Balanced chemical equation for iron reacting with steam:
$$3\text{Fe(s)} + 4\text{H}_2\text{O(g)} \rightarrow \text{Fe}_3\text{O}_4\text{(s)} + 4\text{H}_2\text{(g)}$$
Why iron cannot replace magnesium in a reaction with cold water:
Iron is much less reactive than magnesium. Magnesium reacts readily with hot water to produce hydrogen gas, whereas iron does not react with cold water or even hot water — it reacts only with steam at high temperatures. Therefore, iron cannot be used in the laboratory to produce hydrogen gas by reacting with cold water.
Source: Chapter 3, Section 3.2.2
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Explanation
- The equation for iron + steam is a standard board exam question. Ensure the formula Fe₃O₄ (not Fe₂O₃) is written correctly and the equation is balanced: 3 Fe, 4 H₂O, 1 Fe₃O₄, 4 H₂.
- The second part tests your understanding of the reactivity series: Mg > Fe. Iron reacts only with steam (needs high temperature), not cold or hot water, so it cannot produce H₂ conveniently in the lab.
- Examiners award 1 mark for the balanced equation and 2 marks for the explanation comparing reactivity of iron and magnesium with water.