NCERT Solutions for Class 7 Science Chapter 5 Physical and Chemical Changes

Science is the most practical subject that inspires curiosity and helps students understand the world through real-life experiences. In Class 7, students explore how the world around them works through exciting experiments and real-life examples. It helps them understand daily life in a logical and scientific way.

Chapter 5 of Class 7 Science textbook, titled Physical and Chemical Changes, is an important part of the CBSE Class 7 Science syllabus. This chapter explains the difference between physical changes (where the substance doesn’t change) and chemical changes (where a new substance is formed).

Through the NCERT Solutions Class 7 Science, students can easily revise key points and solve NCERT textbook questions.

NCERT Solutions Class 7 Science Chapter 5 Physical and Chemical Changes

Chapter 5 of Class 7 Science introduces students to the fascinating world of material changes and helps them understand how these changes happen all around us—often without us noticing.

This chapter focuses on two main types of changes: physical changes, where the substance remains the same, and chemical changes, where a new substance is formed. By learning how to identify these changes, students can understand everyday phenomena like the melting of ice, rusting of iron, or the formation of curd.

The chapter also discusses real-life examples, simple experiments, and practical applications. It plays a big role in building a strong foundation for future science topics and helps students prepare effectively for CBSE Class 7 examinations.

With the help of NCERT textbook questions and solutions, students can revise easily and practice important concepts through well-structured answers and exercises. This chapter not only boosts scientific understanding but also encourages curious thinking and observation skills.

Physical Changes

A physical change is a change where the shape, size, or state of a substance may change, but the substance itself remains the same.
These changes are usually temporary and reversible.

Examples:

• Melting of ice
• Breaking of glass
• Dissolving salt in water

In all these cases, no new substance is formed. You can reverse the process in most cases.

Chemical Changes – Definition and Examples

A chemical change happens when one or more substances react to form a completely new substance with different properties. This type of change is usually permanent and cannot be reversed easily.

Examples:

• Rusting of iron
• Burning of paper
• Cooking of food

In a chemical change, the original substance cannot be brought back. This chapter explains how chemical reactions take place and how we observe changes in color, temperature, or gas release.

NCERT Solutions for Class 7 Science Chapter 5 Download Free PDF 

Are you someone who often get jumbled after writing two lines of the answer? To avoid this in exam we have designed accurate answers to your Class 7 Science Chapter 5 questions. Download the NCERT Solutions for Chapter 5 – Physical and Chemical Changes in PDF format and make your exam preparation simple and effective. These solutions are designed to help students understand key concepts, practice important questions, and prepare confidently for the CBSE Class 7 Science exams. 

Each answer is explained in simple way, following the latest NCERT textbook guidelines. Whether you're revising before a test or solving homework, this PDF is a handy resource you can access anytime, anywhere. 

NCERT Class 7 Science Chapter 5 – Physical and Chemical Changes Textbook Questions

1. Identify whether the following activities involve a physical change or a chemical change:

• Photosynthesis – Chemical change (New substances like glucose and oxygen are formed.)
• Dissolving sugar in water – Physical change (No new substance is formed; it can be reversed.)
• Burning of coal – Chemical change (Produces ash and gases; irreversible.)
• Melting of wax – Physical change (Change in state only; can be reversed.)
• Beating aluminium to make foil – This is a physical change because only the shape of the aluminium changes. Its original properties and composition remain the same.
• Digestion of food – Chemical change (New substances are formed through breakdown and absorption).

2. Write the following statements as true or false. If false, explain why.

• Chopping wood into smaller pieces changes its chemical structure.
  False. Cutting wood changes only its size and shape, not the substance itself. So, it's a physical change.
• When dry leaves turn into manure, it's a physical change.
  False. The leaves break down and form a new substance (manure), so it's a chemical change.
• Zinc-coated iron pipes are less likely to rust.
  True. The zinc layer acts as a barrier that keeps moisture and air away from the iron, preventing rust.
• Iron and rust are exactly the same.
  False. Rust is a new substance formed when iron reacts with water and oxygen. They have different properties.
• Steam turning into water is a chemical change.
  False. This is a physical change because only the state of water changes—from gas to liquid—and no new substance is formed.

3. Fill in the blanks:

• Lime water turns milky when carbon dioxide is bubbled through it because it forms a new substance called calcium carbonate.
• Baking soda is chemically known as sodium hydrogen carbonate.
• Two methods to prevent rusting of iron are painting and galvanizing.
• Changes in which only physical properties change are called physical changes.
• Changes in which new substances are formed are called chemical changes.

4. What kind of change occurs when baking soda is mixed with lemon juice?
This is a chemical change. When baking soda and lemon juice react, they form a new substance—carbon dioxide gas—which is seen as bubbles.

5. What types of changes occur when a candle burns?
Melting of wax – Physical change (It only changes state from solid to liquid.)

Burning of wax – Chemical change (Produces new substances like carbon dioxide and soot.)

Another example:
LPG – When released, it changes from liquid to gas (physical change). When it burns, it forms new substances (chemical change).

6. How does the setting of curd show a chemical change?
When milk turns into curd with the help of a sour substance, a new substance is formed. This change is irreversible, which means you can’t turn curd back into milk. Hence, it is a chemical change.

7. How is burning wood different from simply cutting it into smaller pieces?
Burning and cutting wood are different because they involve different types of changes.
When you burn wood, it produces smoke, ash, and gases, which are all new substances. This makes it a chemical change.
On the other hand, cutting wood only changes its shape and size. The wood stays the same material, so it's a physical change.

8. How are crystals of copper sulphate prepared?

• Heat water in a beaker and add a few drops of dilute sulphuric acid.
• Add copper sulphate powder slowly while stirring until no more dissolves.
• Filter the solution and let it cool.

9. Why does painting an iron gate help protect it from rusting?
When iron is exposed to air and moisture, it reacts and forms rust. Painting the iron gate creates a protective layer that blocks air and water from coming into contact with the metal. This barrier prevents rust from forming, keeping the gate strong and durable.

10. Why do iron objects rust more quickly near the sea than in dry areas?
Coastal areas have high humidity because of the sea, meaning more water vapor is present in the air. This moist environment speeds up rusting on iron surfaces. In contrast, deserts have dry air with very little moisture, so rusting happens much more slowly there.

11. In the case of LPG (Liquefied Petroleum Gas), which process shows a chemical change?

When LPG leaves the cylinder, it turns from a liquid to a gas. This is a physical change because the substance stays the same.
When LPG burns, it reacts with oxygen and produces new substances like carbon dioxide and heat, making it a chemical change.

Correct answer: (ii) Burning LPG is a chemical change.

12. Biogas formation and burning – What type of changes are these?

• Process A (digestion by bacteria to form biogas) – Chemical change.
• Process B (burning biogas) – Chemical change.

Correct answer: (iii) Both processes A and B are chemical changes.