CBSE Class 7 Science Chapter 5: Changes Around Us: Physical and Chemical Important Questions by PW

Changes Around Us: Physical and Chemical introduces you to the changes that take place in everyday materials. You may find it difficult to distinguish between physical and chemical changes, understand which changes can be reversed, or identify the signs of a chemical reaction. Examples such as rusting, burning, food spoilage and mixing vinegar with baking soda help you connect these concepts with daily life.

CBSE Class 7 Science Chapter 5 Important Questions by PW help you practise these concepts through 1, 2, 3 and 5 mark questions. The questions cover reversible and irreversible changes, rusting, lime water tests and experiment-based examples, with answers to support revision and school exam preparation.

CBSE Class 7 Science Chapter 5 Important Questions

Chapter 5, Changes Around Us: Physical and Chemical, teaches you how to tell different changes apart. The questions below are grouped by marks, so you can practise short and long answers. 

1 Mark Questions

Q1. Differentiate between a physical change and a chemical change.

Answer: A physical change is temporary. The substance changes its form, but its chemical composition stays the same. A chemical change is permanent. A new substance with different properties is formed.

Q2. Name two types of changes based on reversibility.

Answer: Reversible changes and irreversible changes.

Q3. Give one example of a reversible change from your daily life.

Answer: Melting of ice, boiling of water or dissolving sugar in water.

Q4. What is evaporation?

Answer: Evaporation is the process in which water changes from liquid to vapour because of heat.

Q5. Why is the bursting of a firecracker considered a chemical change?

Answer: New substances (gases, heat and light) are produced. These cannot be converted back to the original cracker.

Q6. What is the chemical name of rust?

Answer: The chemical name of rust is hydrated iron (III) oxide.

Q7. What do you observe when you pass carbon dioxide gas through lime water?

Answer: The lime water turns milky. This happens because calcium carbonate is formed.

2 Mark Questions

Q8. Differentiate between reversible and irreversible changes with examples.

Answer: A reversible change can be undone, like ice melting into water. An irreversible change cannot be undone, like fruit ripening.

Q9. Describe one way in which heat affects matter.

Answer: Heat can make matter change its state. For example, ice melts into water when it is heated.

3 Mark Questions

Q10. Explain why mixing vinegar and baking soda is a chemical change. What evidence supports this?

Answer: Vinegar (acetic acid) and baking soda (sodium hydrogen carbonate) form a new substance, carbon dioxide gas. So it is a chemical change. The evidence is the fizzing sound and the gas bubbles, which were not present in the original substances. This is an irreversible reaction.

You can also revise acids with the Class 7 Science Chapter 2 important questions.

Q11. Iron gates are often painted. Explain the reason in terms of chemical changes.

Answer: Iron gates are painted to prevent rusting. Rusting is a chemical change in which iron reacts with oxygen and moisture in the air to form rust. A layer of paint stops the iron surface from touching oxygen and moisture. This protects the gate from an undesirable chemical change. The Class 7 Science Chapter 4 important questions also cover rusting in more detail.

Q12. Classify the following changes as physical or chemical. Justify your answer for each: (a) melting of a chocolate bar, (b) burning of wood, (c) digestion of food.

Answer:

• (a) Melting of a chocolate bar: This is a physical change. The chocolate changes from solid to liquid, but its chemical composition stays the same. It can be easily reversed by cooling.

• (b) Burning of wood: This is a chemical change. Wood reacts with oxygen to form new substances such as ash, carbon dioxide and water vapour. It is an irreversible change.

• (c) Digestion of food: This is a chemical change. Enzymes break the food down into simpler substances. These new substances can be absorbed by the body. It is an irreversible process.

CBSE Class 7 Science Chapter 5  Important Questions PDF

The PDF is made for Class 7 Chemistry and covers Changes Around Us: Physical and Chemical important questions. It has three sections: very short answer questions of 1 mark each, short answer questions of 3 marks each and long answer questions of 5 marks each. The hint and solution part follows the questions.

A PDF lets you practise even when you are offline. It keeps the questions and solutions together in one file.

How Can CBSE Class 7 Science Chapter 5 Important Questions Help You?

Practising these questions helps you spot the type of change in any example. They can support your preparation in the following ways:

• Tell physical and chemical changes apart: Learn that a physical change is temporary, while a chemical change forms a new substance.

• Know the signs of a chemical change: Remember clues such as fizzing, gas bubbles, a change in smell, a milky white precipitate and the growth of fungus.

• Understand reversible and irreversible changes: Connect ice melting with reversible changes and fruit ripening with irreversible ones.

• Learn about rusting: See why iron gates are painted and how paint keeps out oxygen and moisture.

• Practise experiment-based answers: Questions like Q13 teach you to write observations, reasons and conclusions in order.

• Handle real-life questions: Questions like Q14 show how bread spoilage is linked to moisture, warmth and open air.

Start by looking at where the chapter fits in the CBSE Class 7 Science syllabus. After practice, go back to the CBSE Class 7 Science notes for any answer you missed. The Class 7 Science topic notes explain each idea in more detail.

Your textbook exercises matter too. Compare your answers with the NCERT solutions for Class 7 to see how a full answer is written.

Regular practice helps you understand physical and chemical changes and their real-life examples. Revise these important questions and explore PW’s School Prep courses for additional guidance and practice to prepare confidently for your exams.