Q1. [2] medium thorough-understanding
The balanced equation for the reaction of iron with steam is: 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g). Why is the symbol (g) used for water here instead of (l), even though water is normally a liquid at room temperature?
Generated by claude-sonnet-4-6 · 2026-06-26 00:53 · grounding rag
Model Answer
The symbol (g) is used with H₂O because in this reaction, water is not in liquid form but is used as steam (water vapour). Since the reaction requires high temperature, water exists in the gaseous state. The notation (g) indicates this physical state accurately, making the equation more informative.
Source: Chapter 1, Section 1.1.2 – Writing Symbols of Physical States
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Explanation
- The textbook explicitly states: "the symbol (g) is used with H₂O to indicate that in this reaction water is used in the form of steam."
- Examiners expect two key points: (1) water is in the form of steam/vapour due to high temperature, and (2) (g) denotes gaseous state, not liquid.
- Do not just say "water is heated" — say it is used as steam, which is the gaseous state.