Class 6 Science Chapter 6: Changes Around Us Notes and Questions Answers

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Welcome to Class 6 Science Chapter 6: Changes Around Us. In this page, you will find easy-to-understand notes and NCERT questions & answers with extra practice sets like MCQ, Very Short, Short and Long Questions. These notes are designed for exam preparation and revision. The language is simple, covering all important concepts of reversible and irreversible changes, slow and fast changes, physical and chemical changes, expansion and contraction, and day-to-day examples.

📘 Notes of Class 6 Science Chapter 6: Changes Around Us

Introduction

We see many things changing around us in our daily life. Ice melts, water evaporates, paper is burnt, clothes are ironed, clay is molded into pots, and so on. Some changes are temporary while others are permanent. This chapter helps us to classify and understand these changes scientifically.

Types of Changes

  • Reversible Changes: Changes that can be reversed to get back the original substance. Example – Ice to water and back, stretching of rubber band, inflating a balloon.
  • Irreversible Changes: Changes that cannot be reversed. Example – Burning of paper, cooking of food, rusting of iron.
  • Slow Changes: Changes that take a long time to occur. Example – Growth of a plant, rusting of iron, rotting of fruit.
  • Fast Changes: Changes that occur in very little time. Example – Bursting of crackers, blowing up a balloon, melting of ice.
Class 6 Science Chapter 6 Changes Around Us Notes and Questions Answers | NCERT Solutions
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Physical and Chemical Changes

  • Physical Change: Only physical properties like shape, size, or state change but no new substance is formed. Example – Melting of ice, tearing of paper, boiling of water.
  • Chemical Change: A new substance is formed and the change is usually permanent. Example – Burning of wood, cooking of rice, digestion of food.

Expansion and Contraction

On heating, most materials expand (increase in size). On cooling, they contract (decrease in size). Example – Metal lids are loosened by heating, railway tracks have gaps to allow expansion in summers, power lines sag more in summer due to expansion.

Changes Caused by Heating

  • Ice → Water (reversible)
  • Water → Steam (reversible)
  • Baking of cake (irreversible)
  • Burning of candle wick (irreversible)

Changes Caused by Mixing

  • Sugar in water (reversible)
  • Salt in water (reversible)
  • Vinegar with baking soda (irreversible, gas released)

Importance of Understanding Changes

By learning about changes, we can use them in our daily life. Farmers understand how plants grow (slow changes), engineers design machines that can bear expansion and contraction, and cooks apply heat to prepare food. These examples show how science helps us in practical life.

📝 Questions and Answers of Class 6 Science Chapter 6: Changes Around Us

👉 Multiple Choice Questions (MCQ)

  1. Which of the following is a reversible change?
    a) Burning of paper
    b) Melting of ice
    c) Cooking of rice
    d) Rusting of iron
    Answer: b) Melting of ice
  2. Which of these is an irreversible change?
    a) Freezing of water
    b) Dissolving sugar in water
    c) Burning of candle
    d) Boiling of milk
    Answer: c) Burning of candle
  3. A fast change among the following is:
    a) Growth of a tree
    b) Bursting of firecracker
    c) Rusting of iron
    d) Formation of coal
    Answer: b) Bursting of firecracker
  4. Which one is a chemical change?
    a) Cutting of wood
    b) Melting of wax
    c) Burning of wood
    d) Folding paper
    Answer: c) Burning of wood
  5. Expansion of metal on heating is an example of:
    a) Chemical change
    b) Irreversible change
    c) Physical change
    d) Slow change
    Answer: c) Physical change
  6. Which is a slow change?
    a) Inflating a balloon
    b) Melting ice
    c) Growth of nails
    d) Bursting cracker
    Answer: c) Growth of nails
  7. Rusting of iron requires:
    a) Air only
    b) Water only
    c) Both air and water
    d) Fire
    Answer: c) Both air and water

👉 Very Short Answer Questions

  1. What is a reversible change?
    Answer: A change that can be undone to get the original substance back.
  2. Give one example of irreversible change.
    Answer: Burning of paper.
  3. Name one fast and one slow change.
    Answer: Fast – Bursting of balloon; Slow – Growth of a plant.
  4. Is melting of wax reversible or irreversible?
    Answer: Reversible.
  5. What is contraction?
    Answer: Decrease in size of a substance when cooled.
  6. Give an example of change by mixing.
    Answer: Salt dissolving in water.
  7. Which change takes place when milk turns into curd?
    Answer: Chemical and irreversible change.

👉 Short Answer Questions

  1. Differentiate between reversible and irreversible changes with examples.
    Answer: Reversible changes can be undone (e.g., freezing of water), whereas irreversible changes cannot be undone (e.g., burning of wood).
  2. Why are gaps left in railway tracks?
    Answer: To allow expansion of metal in summers and prevent bending.
  3. Why is rusting harmful?
    Answer: Rusting weakens iron objects and reduces their strength and durability.
  4. Explain with example: Mixing can cause both reversible and irreversible changes.
    Answer: Sugar in water (reversible), vinegar and baking soda (irreversible).
  5. Give one example each of physical and chemical change in the kitchen.
    Answer: Physical – Melting butter; Chemical – Cooking vegetables.
  6. Why do electric wires sag more in summer?
    Answer: Because metals expand on heating and the wires become loose.
  7. Is tearing of paper a physical or chemical change? Explain.
    Answer: It is a physical change because no new substance is formed.

👉 Long Answer Questions

  1. Explain slow and fast changes with four examples of each.
    Answer: Slow changes take time (rusting, growth of plant, ripening of fruit, weathering of rocks). Fast changes are quick (bursting crackers, lighting a match, melting ice, inflating balloon).
  2. What is the difference between physical and chemical changes? Give three examples of each.
    Answer: In physical change, no new substance is formed (melting wax, boiling water, breaking chalk). In chemical change, new substances are formed (burning paper, cooking food, rusting iron).
  3. Explain expansion and contraction with daily life applications.
    Answer: Metals expand when heated and contract on cooling. Gaps in railway tracks, hot lids loosening on jars, and sagging wires are examples of expansion and contraction in daily life.
  4. Why is it important to study changes around us?
    Answer: It helps us understand natural processes, make use of changes in technology, prevent damage (like rusting), and apply knowledge in cooking, farming, and industries.
  5. How does heating cause both reversible and irreversible changes? Give examples.
    Answer: Heating ice forms water (reversible), but heating dough forms roti (irreversible). Thus, heating may or may not form new substances.
  6. Discuss chemical changes in detail with examples.
    Answer: Chemical changes are permanent and form new substances. Examples: Burning wood forms ash and gases; rusting forms rust; milk turning to curd forms lactic acid. These cannot be reversed.
  7. Classify the following as reversible or irreversible with reasons: boiling milk, baking cake, freezing water, bursting cracker, inflating balloon, cutting wood, rusting iron.
    Answer: Boiling milk – Reversible; Baking cake – Irreversible; Freezing water – Reversible; Bursting cracker – Irreversible; Inflating balloon – Reversible; Cutting wood – Physical but irreversible in practice; Rusting iron – Irreversible.