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Tamil Nadu (TNBSE)Class 7 Science★ 6-10 marks in the TN Class 7 Term 2 exam through book-back MCQs, analogies and short answers

Changes Around Us

Samacheer Kalvi (TN State Board) Class 7 Science — Term 2 Chapter 3, Changes Around Us. Physical and chemical changes, reversible and irreversible changes, periodic and non-periodic changes, change of state, and rusting as an irreversible chemical change, with the actual book-back questions, common mistakes and quick revision.

⏱ 14 min readEasy difficulty✓ Free · NCERT-aligned

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The chapter at a glance

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Study Guide

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Key points, glossary and the questions most likely to show up.

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By the end of this chapter you'll be able to…

1Differentiate physical and chemical changes
2Differentiate reversible and irreversible changes
3Differentiate periodic and non-periodic changes
4Explain the change of state as physical
5Describe rusting and its conditions

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Why this chapter matters

Changes Around Us explains how to classify the changes we see every day — vital chemistry vocabulary. Physical vs chemical, reversible vs irreversible and rusting are directly tested book-back content in the TN Class 7 Term 2 exam.

Before you start — revise these

A 5-minute refresher here will save you 30 minutes of confusion below.

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Class 6 — Changes

Types of change.

Changes Around Us — Class 7 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 7 Science, Term 2 — Chapter 3. The many kinds of change.

1. About this chapter

This chapter covers physical and chemical changes, reversible and irreversible changes, periodic and non-periodic changes, change of state, and rusting.

2. Physical and chemical changes

A physical change changes only the state, shape or size of a substance; no new substance is formed (e.g. melting ice, cutting wood into sawdust, colouring paper).
A chemical change forms a new substance with new properties (e.g. wood burning to ash, ripening of fruit, rusting of iron).
The change of state (solid → liquid → gas) is a physical change.

3. Reversible and irreversible changes

A reversible change can be undone — e.g. cold milk heated to become hot can cool again.
An irreversible change cannot be undone — e.g. artificial ripening of fruit and rusting are irreversible chemical changes.

4. Periodic, non-periodic changes and rusting

A periodic change repeats at regular intervals (the change of period in school, day and night); a non-periodic change does not follow a pattern (a forest fire, an earthquake).
Rusting: the brown deposit on iron (e.g. a cycle handle) is rust; rusting is an irreversible chemical change that needs air (oxygen) and moisture.

5. Worked examples

Example 1. Is melting of ice a physical or chemical change? A physical change (change of state, no new substance).

Example 2. What type of change is rusting? An irreversible chemical change.

Example 3. Cold milk heated to become hot — reversible or irreversible? Reversible.

6. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

Rusting of iron is — (a) a physical change / (b) an irreversible chemical change. Ans: (b) irreversible chemical change.
The change of state from solid to liquid and liquid to gas is — (a) a physical change / (b) a chemical change. Ans: (a) physical change.

II. Fill in the blanks / Analogy 3. The brown deposit on a cycle handle is due to rusting, which is a chemical change. 4. Wood to sawdust : physical change :: wood to ash : chemical change. 5. Change of period in school : periodic change :: forest fire : non-periodic change.

III. Answer briefly 6. What type of change is the artificial ripening of fruit? — An irreversible chemical change. 7. What type of change is colouring a paper? — A physical change. 8. What two things are needed for rusting? — Air (oxygen) and moisture.

7. Common mistakes

Mistake: Calling rusting a physical change. Fix: Rusting forms a new substance (rust) — it is a chemical (and irreversible) change.
Mistake: Thinking all changes can be reversed. Fix: Irreversible changes (rusting, ripening, burning) cannot be undone.
Mistake: Confusing periodic and non-periodic. Fix: Periodic repeats regularly (day/night); non-periodic has no pattern (a forest fire).

8. Quick revision

Term 2 · Ch 3 · changes around us.
Physical change: no new substance (melting, cutting, colouring); change of state is physical.
Chemical change: new substance (burning, ripening, rusting).
Reversible (heating milk) vs irreversible (rusting, ripening); periodic (day/night) vs non-periodic (forest fire).
Rusting = irreversible chemical change needing air and moisture.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Physical change

no new substance (state/shape/size)

Change of state is physical.

Chemical change

new substance formed

Burning, ripening, rusting.

Reversible vs irreversible

can be undone vs cannot be undone

Heating milk vs rusting.

Rusting

irreversible chemical change; needs air + moisture

Brown rust on iron.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Calling rusting a physical change

✓ Rusting forms a new substance (rust) — it is a chemical and irreversible change.

WATCH OUT

✗ Thinking all changes can be reversed

✓ Irreversible changes (rusting, ripening, burning) cannot be undone.

WATCH OUT

✗ Confusing periodic and non-periodic

✓ Periodic repeats regularly (day/night); non-periodic has no pattern (a forest fire).

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Choose the correct answer

Book-back MCQs on rusting and change of state.

Questions

Analogies / Fill in the blanks

Rusting, physical vs chemical and periodic vs non-periodic.

Questions

Answer briefly

Ripening, colouring paper and conditions for rusting.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· MCQ

Rusting of iron is which type of change?

▶ Show solution

An irreversible chemical change.

Q2EASY· MCQ

The change of state from solid to liquid is which type of change?

▶ Show solution

A physical change.

Q3EASY· Analogy

Wood to sawdust : physical change :: wood to ash : ____.

▶ Show solution

chemical change.

Q4EASY· Answer briefly

What type of change is the artificial ripening of fruit?

▶ Show solution

An irreversible chemical change.

Q5EASY· Answer briefly

What type of change is colouring a paper?

▶ Show solution

A physical change.

Q6MEDIUM· Answer briefly

What two conditions are needed for rusting, and what kind of change is it?

▶ Show solution

Rusting needs air (oxygen) and moisture, and it is an irreversible chemical change.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Term 2 Chapter 3 of Samacheer Kalvi Class 7 Science.
•Physical change: no new substance (melting, cutting, colouring); change of state is physical.
•Chemical change: a new substance forms (burning, ripening, rusting).
•Reversible change can be undone (heating milk); irreversible cannot (rusting, ripening).
•Periodic change repeats regularly (day/night); non-periodic has no pattern (forest fire).
•Rusting is an irreversible chemical change needing air (oxygen) and moisture.

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 6-10 marks across book-back MCQ, analogies and short answers

Question type	Marks each	Typical count	What it tests
MCQ / Analogy	1	3-5	Types of change
Short Answer	1-2	2-3	Ripening, rusting, colouring

Prep strategy

Ask 'is a new substance formed?' for chemical change
Test if the change can be undone (reversible)
Check for a regular pattern (periodic)
Remember rusting needs air and moisture

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Preservation

Preventing rust protects tools, vehicles and bridges.

Cooking

Many cooking changes are irreversible chemical changes.

Recycling

Reversible physical changes allow materials to be reused.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Check for a new substance (chemical change)
Test reversibility
Look for a regular pattern (periodic)
Quote air + moisture for rusting

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Classify five everyday changes as physical or chemical with reasons.
Suggest three ways to prevent the rusting of iron.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 7 Term 2 ExamHigh

NMMS / Foundation ScienceMedium

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

Ask whether a new substance with new properties is formed: if yes (like wood turning to ash) it is a chemical change; if only the state, shape or size changes (like ice melting) it is a physical change.

Rusting turns iron into a new substance (iron oxide) that cannot be turned back into iron by simple means, so it is an irreversible chemical change.

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