Write balanced chemical equation for the reactions that occur when
(a) steam is passed over red hot iron.
(b) natural gas is burnt in air.
(c) glucose reacts with oxygen in the cells of our body and provides energy.
Generated by claude-sonnet-4-6 · 2026-06-14 10:28 · grounding rag
Model Answer
(a) Steam passed over red hot iron:
$$3\text{Fe}(s) + 4\text{H}_2\text{O}(g) \rightarrow \text{Fe}_3\text{O}_4(s) + 4\text{H}_2(g)$$
(b) Natural gas (methane) burnt in air:
$$\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(g) + \text{heat and light}$$
(c) Glucose reacting with oxygen in body cells:
$$\text{C}_6\text{H}_{12}\text{O}_6(aq) + 6\text{O}_2(g) \rightarrow 6\text{CO}_2(g) + 6\text{H}_2\text{O}(l) + \text{energy}$$
Source: Chapter 1 – Chemical Reactions and Equations; Chapter 4 – Carbon and its Compounds, Section 4.3.1
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Explanation
- (a) is a displacement/redox reaction — iron displaces hydrogen from steam forming iron oxide (Fe₃O₄). Students often forget the coefficient 4 on both H₂O and H₂.
- (b) Natural gas = methane (CH₄). The balanced equation requires coefficient 2 before O₂. Always mention heat and light for combustion.
- (c) This is cellular respiration — an exothermic reaction. Write "energy" (not just heat) as the product. Balancing correctly (6 on O₂, CO₂, and H₂O) is key for full marks.
- Each equation carries 1 mark — a missing or wrong coefficient loses the mark, so double-check balancing.