Q1. [2] medium thorough-understanding
A student argues: 'When we cook food, no new substance is formed — it just gets soft and changes texture, so it is a physical change.' Using your understanding of chemical reactions, explain why this argument is incorrect.
Generated by claude-sonnet-4-6 · 2026-06-26 00:53 · grounding rag
Model Answer
The student's argument is incorrect. Cooking food is a chemical change, not physical. During cooking, new substances are formed due to breaking and making of bonds between atoms. Indicators like change in colour, change in smell, and irreversibility confirm a chemical reaction has occurred. The change cannot be reversed, unlike physical changes.
Source: Chapter 1 – Chemical Reactions and Equations, Chapter Introduction
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Explanation
- The textbook explicitly lists cooking food as an example where "the nature and identity of the initial substance have somewhat changed" — i.e., a chemical reaction occurs.
- Key examiner expectation: state that new substances are formed (bonds broken and made) and give evidence of chemical change (irreversibility, change in colour/smell).
- Don't just say "it is a chemical change" — briefly justify why with at least one indicator. That earns both marks.