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ICSE Class 7 Chemistry Question 13 of 13

Physical and Chemical Changes — Question 13

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Question

Question 5i

When we add water to the following substances, which one will show a chemical change?

  1. salt
  2. sugar
  3. oil
  4. quick lime
Answer

quick lime

Reason — Quick lime reacts with water to form calcium hydroxide and a large amount of heat is produced which is a chemical change.

Source: This question is from Physical and Chemical Changes, Chemistry — Class 7, ICSE Board.

Key Concepts Covered

This question tests your understanding of the following concepts from the chapter Physical and Chemical Changes: Question, Add, Water, Substances, Chemical, Change. These are fundamental topics in Chemistry that students are expected to master as part of the ICSE Class 7 curriculum.

A thorough understanding of these concepts will help you answer similar questions confidently in your ICSE examinations. These topics are frequently tested in both objective and subjective sections of Chemistry papers. We recommend revising the relevant section of your textbook alongside practising these solved examples to build a strong foundation.

How to Approach This Question

Read the question carefully and identify what is being asked. Break down complex questions into smaller parts. Use the terminology and concepts discussed in this chapter. Structure your answer logically — begin with a definition or key statement, then provide supporting details. Review your answer to ensure it addresses all parts of the question completely.

Key Points to Remember

  • Balance chemical equations before solving numerical problems.
  • Learn the periodic table trends and exceptions.
  • Understand reaction mechanisms, not just outcomes.
  • Use correct IUPAC nomenclature in your answers.

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ICSE Class VII Chemistry Chapter 2 12 Marks

Physical and Chemical Changes — Quick Study Guide

Changes around us are classified as physical (no new substance formed) or chemical (new substance formed). Understanding the difference is fundamental to chemistry.

Key Definitions

  • Physical change: No new substance formed, usually reversible (e.g., melting ice, dissolving sugar)
  • Chemical change: New substance formed, usually irreversible (e.g., burning, rusting, cooking)
  • Exothermic: Reaction that releases heat (e.g., burning fuel)
  • Endothermic: Reaction that absorbs heat (e.g., photosynthesis)

Six Signs of Chemical Change

Colour change, gas evolution, temperature change, precipitate formation, smell change, light/sound emission.

Exam Tips

  • Burning a candle = BOTH physical and chemical change
  • Dissolving salt/sugar in water = physical change (recoverable)
  • Not all physical changes are reversible (tearing paper)
  • Learn the comparison table (6 differences) thoroughly

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