Class 7 · NCERT Science

Chapter 5

Physical and Chemical Changes

Compare physical and chemical changes with observations. Learn the ideas, see how they connect, and practise until you can choose the next step without help.

Physical changeChemical changeRusting

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Study board

Quick reference
Concept 01Physical change
Concept 02Chemical change
Concept 03Rusting

NCERT chapter notes

Physical and Chemical Changes, clearly explained

Physical and Chemical Changes asks students to decide whether only physical properties changed or whether one or more new substances formed. The chapter uses crystallisation, rusting, burning, and common reactions to make that distinction observable.

Reversibility can be a clue, but it is not the complete definition. The strongest evidence for chemical change is the formation of a substance with new properties, often accompanied by gas, precipitate, heat, light, smell, or colour change.

Core concepts

Key concepts and formulae

01

Physical change

A physical change alters shape, size, state, or appearance without forming a new substance. Melting ice and cutting paper are examples, though reversibility may differ.

02

Chemical change

A chemical change forms one or more new substances with different properties. Burning magnesium forms magnesium oxide; vinegar and baking soda produce carbon dioxide along with other products.

03

Rusting of iron

Rust forms when iron reacts with oxygen in the presence of water. Rusting can be reduced by painting, oiling, greasing, galvanising, or keeping iron away from air and moisture.

04

Crystallisation

Crystallisation separates a pure solid in the form of crystals from its solution. It is useful when simple evaporation may leave impurities or damage the substance.

Exam practice

Important questions, with worked answers

Use each answer to check the method and wording—not as a paragraph to memorise.

Q1Why is burning magnesium ribbon a chemical change?

Answer

Magnesium reacts with oxygen and forms magnesium oxide, a new white substance with properties different from magnesium.

Q2What conditions are necessary for rusting of iron?

Answer

Both oxygen from air and water or moisture are necessary for iron to rust.

Q3How does galvanisation protect iron?

Answer

Iron is coated with zinc, which keeps air and moisture away from the iron surface and therefore prevents rusting.

Q4Why is crystallisation better than simple evaporation for purifying some solids?

Answer

Crystallisation can produce purer solid crystals while leaving many impurities in solution and avoiding excessive heating that may decompose the substance.

Fast recall

Key terms to remember

Physical change: A change in physical properties without formation of a new substance.

Chemical change: A change that forms one or more new substances.

Rust: A reddish-brown hydrated iron oxide formed when iron reacts with oxygen and moisture.

Crystallisation: The process of obtaining pure solid crystals from a solution.

A repeatable method

How to learn Physical and Chemical Changes properly

  1. 1

    Start with the chapter promise

    Compare physical and chemical changes with observations. Before solving, the student should be able to say what the chapter is trying to teach and which kind of problem it helps solve.

  2. 2

    Build the core vocabulary

    The important words for this chapter are Physical change, Chemical change and Rusting. Eduro should make the student define each one in simple language, then use it in a question or explanation.

  3. 3

    Move from recognition to recall

    Recognition means the answer makes sense after seeing it. Recall means the student can produce the next step independently. This page is built for recall, because that is what tests reward.

  4. 4

    Close the loop with practice

    A strong study session ends with concept and diagram practice, not only reading. The student should solve, review the mistake, and then attempt a similar question before moving on.

Before the test

Where students usually lose marks

Look for the first wrong decision—not only the final wrong answer. That is the mistake worth repairing.

Mistake 1

Knowing Physical change only after seeing the solution

This is the most common hidden gap. The student feels confident while reading, but cannot choose the starting step alone. Eduro should ask a short diagnostic question before explaining the method.

Mistake 2

Treating Physical and Chemical Changes as a memory chapter

Even memory-heavy chapters need reasoning. A memorised line becomes fragile when the question changes. The student should explain why the answer works, not only what the answer is.

Mistake 3

Skipping the checking step

concept-to-example gap usually survives because the student finishes the answer and moves on. Eduro should make review part of the answer: what was asked, what was used, and whether the final response fits.

Try it with Eduro

Practice that builds real confidence

Say it naturally, as you would to a patient teacher. Each prompt below is designed to make understanding visible.

Prompt 1

Ask Eduro to explain Physical and Chemical Changes through Physical change before showing any solved answer.

Prompt 2

Create five questions that separately test Physical change, Chemical change and Rusting.

Prompt 3

Give one wrong answer from Physical and Chemical Changes and ask the student to find the first incorrect step.

Prompt 4

End with a mixed mini-test where Eduro does not reveal which skill is being tested.

For parents

A better way to ask, “Is the chapter done?”

For Class 7 Science, a good sign is not that the child says 'Physical and Chemical Changes is done.' A better sign is that they can explain Physical change, solve one fresh question, and correct one mistake without panic.

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Quick help

Common questions

How can I study Physical and Chemical Changes for NCERT Class 7?

Start with the NCERT examples, understand the key ideas in Physical change, Chemical change, Rusting, then practice exercise questions and ask Eduro where you get stuck.

Can Eduro help with Physical and Chemical Changes?

Yes. Eduro can explain Physical and Chemical Changes step by step, answer follow-up doubts, and help students practice related Science questions.