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

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I. Chapter Summary:

This chapter explains different types of changes that occur around us—physical and chemical changes. It helps students understand how substances change in form or composition and how to identify whether a change is reversible or irreversible. The chapter also highlights everyday examples and the importance of chemical reactions in daily life.

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II. Key Concepts Covered:

• Change:
  Any alteration in the state, shape, size, or composition of a substance.
• Physical Change:
  A change in which no new substance is formed.
  Examples: melting of ice, cutting paper
• Chemical Change:
  A change in which a new substance is formed.
  Examples: rusting of iron, burning of paper
• Reversible and Irreversible Changes:
  • Reversible: Can be undone (e.g., melting and freezing)
  • Irreversible: Cannot be undone (e.g., burning)
• Indicators of Chemical Change:
  • Change in color
  • Release of gas
  • Formation of new substance
  • Change in temperature
• Importance of Chemical Changes:
  • Cooking food
  • Digestion
  • Respiration

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III. Important Questions:

(A) MCQs (1 Mark):

1. Physical change forms:
   (a) New substance
   (b) No new substance ✅
   (c) Gas
   (d) Liquid
2. Rusting of iron is a:
   (a) Physical change
   (b) Chemical change ✅
   (c) Temporary change
   (d) Reversible change
3. Reversible change can be:
   (a) Permanent
   (b) Undone ✅
   (c) Chemical
   (d) Irreversible
4. Burning of paper is:
   (a) Reversible
   (b) Physical
   (c) Chemical and irreversible ✅
   (d) Temporary

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IV. Key Formulas/Concepts:

Basic concept of chemical change:

Substance A→Substance B (new substance)text{Substance A} rightarrow text{Substance B (new substance)}Substance A→Substance B (new substance)

• Physical Change → No new substance
• Chemical Change → New substance formed
• Reversible → Can be reversed
• Irreversible → Cannot be reversed

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

1. What is a physical change?
2. What is a chemical change?
3. Give examples of reversible changes.
4. What are indicators of chemical change?

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(C) Long Answer Questions (5 Marks):

1. Explain physical and chemical changes with examples.
2. Differentiate between reversible and irreversible changes.
3. Describe indicators of chemical changes.
4. Explain importance of chemical changes in daily life.

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(D) HOTS Questions:

1. Why is rusting considered a chemical change?
2. Can all physical changes be reversed? Give reasons.

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V. Deleted Portions (CBSE 2025–2026):

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

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

Unit/Chapter	Estimated Marks	Type of Questions Typically Asked
Changes Around Us: Physical and Chemical	6–8 Marks	MCQs, Short Answers, Case-based, Experiment-based

Note: This is an estimate. Actual marks distribution may vary.

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VII. Previous Year Questions (PYQs):

1 Mark:

• What is a physical change? (CBSE 2020)

2/3 Marks:

• Define chemical change. (CBSE 2019)
• Give examples of reversible changes. (CBSE 2021)

5 Marks:

• Differentiate physical and chemical changes. (CBSE 2022)
• Explain importance of chemical changes. (CBSE 2023)

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VIII. Real-World Application Examples:

• Melting ice is a physical change.
• Cooking food is a chemical change.
• Rusting of iron affects buildings and machines.
• Digestion of food is a chemical process.

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IX. Student Tips & Strategies for Success:

Time Management:

• Study physical and chemical changes separately.

Exam Preparation:

• Focus on examples and differences.
• Practice writing clear explanations.

Stress Management:

• Use real-life observations.
• Revise regularly.

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X. Career Guidance & Exploration:

• Science Stream: Chemistry, Chemical Engineering
• Commerce Stream: Industrial Chemistry Management
• Arts Stream: Environmental Studies

Entrance Exams:

• JEE (Engineering)
• NEET (Medical)
• IISER (Research)

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XI. Important Notes:

• Focus on identifying types of changes.
• Learn indicators of chemical changes.
• Use real-life examples for clarity.
• Refer NCERT textbook for accuracy.