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Class 7 Science Chapter 5 Changes Around Us: Physical and Chemical

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I. Chapter Summary:

This chapter introduces the concepts of physical and chemical changes observed in daily life. It explains the difference between these two types of changes based on reversibility and the formation of new substances. Various examples like melting, boiling, burning, and rusting are discussed to help students identify and classify changes. The chapter emphasizes the importance of understanding these changes in natural phenomena and everyday activities.

II. Key Concepts Covered:

• Physical Changes: Changes in the state or appearance of a substance without forming a new substance (e.g., melting, freezing, dissolving).

• Chemical Changes: Changes that result in the formation of one or more new substances with different properties (e.g., burning, rusting, digestion).

• Reversibility: Physical changes are mostly reversible, whereas chemical changes are mostly irreversible.

• Signs of Chemical Changes: Color change, gas evolution, temperature change, formation of precipitate.

• Examples of Physical Changes: Melting of ice, boiling of water, tearing paper.

• Examples of Chemical Changes: Burning of paper, rusting of iron, souring of milk.

III. Important Questions:

(A) Multiple Choice Questions (1 Mark):

1. Which of the following is a physical change?
   a) Burning of paper
   b) Melting of ice
   c) Rusting of iron
   d) Digestion of food
   Answer: b) Melting of ice
   (PYQ 2022)

2. Chemical changes are usually:
   a) Reversible
   b) Irreversible
   c) Temporary
   d) Physical
   Answer: b) Irreversible

3. Which of the following indicates a chemical change?
   a) Boiling water
   b) Tearing paper
   c) Change in color during rusting
   d) Dissolving sugar in water
   Answer: c) Change in color during rusting

4. When water boils, the change is:
   a) Chemical and reversible
   b) Physical and reversible
   c) Chemical and irreversible
   d) Physical and irreversible
   Answer: b) Physical and reversible

(B) Short Answer Questions (2/3 Marks):

1. Define physical change with two examples.

2. What are chemical changes? Give two examples.

3. How can you distinguish between physical and chemical changes?

4. List any two signs of a chemical change.

(C) Long Answer Questions (5 Marks):

1. Explain with examples how physical and chemical changes differ.

2. Describe the process and significance of rusting of iron.

3. Discuss why burning paper is considered a chemical change.

4. Explain why melting of ice is a physical change.

(D) HOTS (Higher Order Thinking Skills) Questions:

1. Can a physical change ever become a chemical change? Explain with an example.

2. Why do some chemical changes release heat while others absorb it? Provide examples.

IV. Key Formulas/Concepts:

• Physical Change: No new substance formed; reversible.

• Chemical Change: New substance formed; mostly irreversible.

• Signs of chemical change: Color change, gas release, temperature change, precipitate formation.

• Examples and definitions as explained above.

V. Deleted Portions (CBSE 2025–2026):

No portions have been deleted from this chapter as per the rationalized NCERT textbooks.

VI. Chapter-Wise Marks Bifurcation (Estimated – CBSE 2025–2026):

VII. Previous Year Questions (PYQs):

• 2023: MCQ on physical changes (1 mark)

• 2021: Short answer on chemical change examples (2 marks)

• 2020: Long answer on difference between physical and chemical changes (5 marks)

• 2019: HOTS on chemical reactions releasing or absorbing heat (3 marks)

VIII. Real-World Application Examples to Connect with Topics:

• Melting ice in cold drinks (physical change).

• Burning of fuel in vehicles (chemical change).

• Rusting of iron in bridges and vehicles (chemical change) and its prevention.

• Boiling water for cooking (physical change).

IX. Student Tips & Strategies for Success:

• Observe daily life changes and try classifying them as physical or chemical.

• Use experiments (if possible) to identify physical and chemical changes.

• Revise signs of chemical changes regularly.

• Practice distinguishing reversible and irreversible changes through examples.

X. Career Guidance & Exploration:

• For Classes 9–10:

  • Foundation for careers in Chemistry, Environmental Science, and related fields.

  • Helpful for NTSE and Science Olympiads preparation.

• For Classes 11–12:

  • Important for students pursuing Chemistry, Biochemistry, Chemical Engineering, Environmental Science, and Medicine.

  • Relevant for entrance exams like NEET, JEE, and CUET.

XI. Important Notes:

• Keep updated with official NCERT and CBSE notifications for syllabus changes.

• Conceptual clarity is essential; avoid rote memorization.

• Use diagrams and examples to strengthen understanding.