CBSE Class 6 Science Chapter 6: Changes Around Us NCERT Solutions

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NCERT Solutions PDF Class 6 PDF

This chapter, "Changes Around Us," for CBSE Class 6 Science, delves into the fundamental concepts of changes that occur in our daily lives. The NCERT Solutions provide clear explanations and examples of both reversible and irreversible changes. Students will learn to identify different types of changes, understand the conditions under which they occur, and differentiate between those that can be undone and those that cannot. The solutions cover exercises that involve practical scenarios like folding clothes, breaking toys, melting ice, cooking food, and the setting of Plaster of Paris. By working through these solutions, students will develop a strong foundation in understanding the nature of physical and chemical changes, which is crucial for further scientific learning. These solutions are designed to aid students in grasping these concepts effectively and preparing for their examinations.

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Quick info

BoardCBSE
ClassClass 6
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 6: Changes Around Us

Chapter summary

Chapter 6, "Changes Around Us," focuses on distinguishing between reversible and irreversible changes. The NCERT Solutions cover exercises that help students identify examples of both types of changes from everyday life. Key concepts include understanding how melting, dissolving, and folding are reversible, while cooking, ripening, burning, and chemical reactions like cement hardening are irreversible. The solutions provide clear reasoning for classifying each change, aiding students in mastering this foundational topic in physical and chemical changes.

Learning outcomes

  • Identify and differentiate between reversible and irreversible changes.
  • Provide examples of reversible changes from daily life.
  • Provide examples of irreversible changes from daily life.
  • Understand the concept of physical and chemical changes.
  • Explain why certain changes cannot be reversed.

Topics covered

Paper topics

  • Changes Around Us
  • Reversible Changes
  • Irreversible Changes
  • Physical Changes
  • Chemical Changes
  • Examples of Reversible Changes
  • Examples of Irreversible Changes
  • Plaster of Paris
  • Cement Hardening
  • Melting and Freezing
  • Dissolving
  • Cooking

Important topics

  • Distinguishing between reversible and irreversible changes
  • Identifying everyday examples of both types of changes
  • Understanding the nature of physical vs. chemical changes
  • The role of chemical reactions in irreversible changes (POP, cement)
  • Reversibility of dissolving and melting

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Questions and Solutions

Question 1

To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Solution: Yes, this change can be reversed. By unfolding the folded part of the dress, you can restore it to its original length.

Question 2

You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?
Solution: No, this change cannot be reversed. Once a toy is broken into pieces, it cannot be easily reassembled to its original, unbroken state. This is an example of an irreversible change.

Question 3

Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not.
  1. No. Change
  2. The sawing of a piece of wood
  3. The melting of ice candy
  4. Dissolving sugar in water
  5. The cooking of food
  6. The ripening of a mango
  7. Souring of milk
Solution: Here is the table completed with whether each change can be reversed:
  1. No. Change | Can be reversed (Yes/No)
  2. The sawing of a piece of wood | No
  3. The melting of ice candy | Yes
  4. Dissolving sugar in water | Yes
  5. The cooking of food | No
  6. The ripening of a mango | No
  7. Souring of milk | No
Explanation: Sawing wood produces smaller pieces that cannot be joined back. Melting ice candy is reversible by freezing. Dissolving sugar is reversible by evaporation. Cooking, ripening, and souring involve chemical changes that are generally irreversible.

Question 4

A drawing sheet changes when you draw a picture on it. Can you reverse this change?
Solution: It depends on how the drawing is made. If you draw with a pencil, the change is reversible because you can erase the drawing using an eraser. However, if you draw with a pen, the ink creates a permanent mark, making the change irreversible as it cannot be easily erased.

Question 5

Give examples to explain the difference between changes that can or cannot be reversed.
Solution: The difference between reversible and irreversible changes can be explained with examples:

Examples of Reversible Changes:

  • Melting of Ice into water: Ice melts to form water, but the water can be frozen back into ice.
  • Folding a paper: A paper can be folded, but it can be unfolded back to its original flat state.
  • Hot milk to cold milk: Hot milk cools down, but it can be heated again.

Examples of Irreversible Changes:

  • Burning of a candle: Once a candle burns, the wax is consumed and cannot be reformed into the original candle.
  • Bursting of crackers: The chemical reaction during bursting cannot be undone.
  • Cutting of trees: A cut tree cannot be restored to its original form.

Question 6

A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed?
Solution: No, the change in Plaster of Paris when it dries cannot be reversed. When water is added to POP, it undergoes a chemical reaction and sets into a hard solid. This is a chemical change where the composition of POP changes, and it cannot be converted back to its original paste form easily.

Question 7

A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?
Solution: No, the changes that have occurred in the cement cannot be reversed. When cement gets wet, it undergoes a chemical reaction with water, causing it to harden. This process is called setting. Once cement has set, it cannot be turned back into its original powdery form. This is an irreversible chemical change.

Common mistakes

  • Confusing physical changes (like folding) with chemical changes (like cooking).
  • Assuming all changes involving liquids (like melting ice) are always reversible without considering the context.
  • Not recognizing that some seemingly irreversible changes (like drawing with a pen) can be irreversible under specific conditions.

Revision tips

  • Create a table listing reversible and irreversible changes encountered daily.
  • Focus on the 'why' behind each classification – what makes a change reversible or not?
  • Relate the concepts to real-life examples discussed in the solutions.
  • Pay close attention to the examples of Plaster of Paris and cement hardening as they illustrate chemical changes.

Practice MCQs

Q1. Which of the following is an example of a reversible change?

Q2. When a drawing is made on a sheet of paper with a pencil, can the change be reversed?

Q3. The change that occurs when food is cooked is:

Q4. What happens when Plaster of Paris (POP) paste dries on a fractured bone?

Q5. Dissolving sugar in water is an example of:

Frequently asked questions

What is the main difference between reversible and irreversible changes?

A reversible change can be undone, meaning the original state can be restored. An irreversible change cannot be undone; the original state cannot be restored.

Are all changes involving liquids reversible?

Not necessarily. For example, melting ice is reversible (water can freeze back to ice), but the change when cement hardens after getting wet is not reversible.

How does drawing with a pencil differ from drawing with a pen in terms of reversibility?

Drawing with a pencil is usually reversible because pencil marks can be erased. Drawing with a pen often results in an irreversible change because ink is difficult or impossible to remove completely.

What kind of change occurs when food is cooked?

Cooking food involves chemical changes that alter its composition and properties, making it an irreversible change.

Can the change in Plaster of Paris when it dries be reversed?

No, the change in Plaster of Paris when it dries and hardens is a chemical change and is irreversible.

Why is dissolving sugar in water considered a reversible change?

Because the sugar can be recovered by evaporating the water, returning to the original solid sugar and liquid water.

Important links

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