ChemistryICSE Class 8 · Chapter 2

Physical and Chemical Changes ICSE Class 8: Differences and Classification

Updated 15 October 2026 · Fact-checked

A physical change alters only the form, size or state of a substance; no new substance forms and it is usually reversible, like melting ice. A chemical change forms new substances with new properties and is usually irreversible, like burning paper. ICSE Class 8 classifies everyday changes using these differences.

What Physical and Chemical Changes is about

Substances around us keep changing: ice melts, iron rusts, milk turns into curd, paper burns. Chemists sort these changes into two groups.

A physical change changes the physical properties (shape, size, state, appearance) of a substance, but no new substance is formed. The composition stays the same, and the change is usually reversible.
A chemical change forms one or more new substances with different properties and a different composition. It is usually irreversible and often involves heat or light being given out or taken in.

The CISCE Class VIII curriculum asks you to revise these ideas from earlier classes and classify changes as physical or chemical with examples. You should also be able to spot the signs of a chemical change: a change of colour, a gas given off, a precipitate formed, heat or light produced, or a change in smell.

Weightage: CISCE publishes no question paper, marking scheme or chapter weightage for Class VIII Chemistry: your school sets and marks the exam. Physical and Chemical Changes sits in the Theme: Physical and Chemical Changes theme of the CISCE Curriculum for Upper Primary Classes (VI-VIII).Source: CISCE Curriculum for Upper Primary Classes (VI-VIII), RDCD 2016

Key concepts

Physical change

In a physical change:

no new substance is formed;
the composition (what the substance is made of) does not change;
only physical properties such as state, shape, size or colour intensity change;
the change is usually reversible by simple means;
there is little or no energy change (except for changes of state).

Examples: melting of ice, boiling of water, dissolving sugar or salt in water, breaking glass, cutting paper, bending a wire, stretching a rubber band, magnetising iron, glowing of an electric bulb filament, sublimation of camphor.

Worked example

Salt is dissolved in water. Why is this a physical change? How can the salt be recovered?

Try it first, then show the solutionSolution

No new substance forms: the solution still tastes salty and contains salt and water.
Evaporating the water leaves the salt behind, so the change can be reversed.

Answer: No new substance and reversible; recover salt by evaporation.

Chemical change

In a chemical change:

new substances are formed with new properties;
the composition changes: atoms are rearranged into new combinations;
the change is usually irreversible;
energy (heat, light or sound) is usually given out or taken in.

Examples: burning of paper, wood, candles or magnesium; rusting of iron; cooking food; curdling of milk; ripening and rotting of fruit; digestion; photosynthesis; respiration; the reaction of iron with copper sulphate solution.

$2 M g + O_{2} \to 2 M g O$ (a bright white flame and a white powder that is not magnesium).

Worked example

Why is burning a piece of paper a chemical change?

Try it first, then show the solutionSolution

New substances form: ash, carbon dioxide and water vapour, which are not paper.
Heat and light are given out, and the ash cannot be turned back into paper.

Answer: New substances form and the change is irreversible.

Signs of a chemical change

Look for these clues:
1. Change in colour (blue copper sulphate solution turns green when iron is added).
2. Gas given off (fizzing when baking soda meets vinegar; carbon dioxide).
3. Precipitate (an insoluble solid) formed when two solutions mix (white barium sulphate).
4. Heat, light or sound produced or absorbed (burning, quicklime and water getting hot).
5. Change in smell or taste (milk turning sour, food rotting).

One clue alone is not proof: boiling water also gives off a gas (steam), but no new substance forms. Ask: is there a new substance?

Worked example

An iron nail is placed in blue copper sulphate solution. After some time the solution turns green and a brown coating forms on the nail. Is this a physical or a chemical change? Write the equation.

Try it first, then show the solutionSolution

The colour change and the brown coating (copper) show new substances: iron sulphate and copper.
So it is a chemical change: $F e + C u S O_{4} \to F e S O_{4} + C u$ .

Answer: Chemical change

Differences between physical and chemical changes

Physical change	Chemical change
no new substance formed	new substance(s) formed
composition unchanged	composition changes
usually reversible	usually irreversible
little or no energy change (except change of state)	heat/light usually given out or taken in
mass of each substance unchanged	substances change, though total mass is conserved
e.g. melting wax, dissolving sugar	e.g. burning wax, rusting

The same substance can undergo both: a burning candle shows melting of wax (physical) and burning of wax vapour (chemical).

Worked example

When a candle burns, which changes are physical and which chemical?

Try it first, then show the solutionSolution

Wax melting near the wick and solidifying again: physical.
Wax vapour burning to carbon dioxide and water with heat and light: chemical.

Answer: Melting is physical; burning is chemical.

Classifying everyday changes

Change	Type	Reason
Melting of butter	physical	only state changes
Curdling of milk	chemical	new substance (curd), sour taste
Rusting of iron	chemical	new brown substance (rust)
Folding paper	physical	only shape changes
Digestion of food	chemical	food broken into new substances
Formation of clouds	physical	water vapour condenses
Cooking an egg	chemical	cannot be uncooked
Glowing of a bulb filament	physical	stops glowing when switched off; no new substance

Note: 'irreversible' alone does not make a change chemical: breaking glass is irreversible but physical.

Worked example

Classify (i) breaking a glass (ii) cooking rice, giving a reason.

Try it first, then show the solutionSolution

(i) Physical: the pieces are still glass; only the shape and size change (though it cannot easily be reversed).
(ii) Chemical: cooked rice has new properties and cannot be changed back.

Answer: (i) Physical (ii) Chemical

Energy changes and mass

Many chemical changes give out heat (burning, quicklime reacting with water) and some take it in (cooking needs heat).

Quicklime (calcium oxide) and water react with a hissing sound and a lot of heat:
$C a O + H_{2} O \to C a (O H)_{2}$ .

In both kinds of change, the total mass is conserved (law of conservation of mass). In a physical change each substance keeps its mass (50 g of ice gives 50 g of water); in a chemical change the masses of the products add up to the masses of the reactants.

Worked example

10 g of salt is dissolved in 100 g of water. What is the mass of the solution? Is the change physical or chemical?

Try it first, then show the solutionSolution

Mass is conserved: $10 + 100 = 110$ g.
No new substance forms and the salt can be recovered: physical change.

Answer: 110 g; physical

Chemistry in real life: Physical and Chemical Changes

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Curdling of milk

Suppose you leave a glass of milk with a spoonful of curd in a warm kitchen overnight.

Is the change physical or chemical? Give two reasons.

Try it first, then show the solutionSolution

The milk becomes thick curd with a sour taste: a new substance with new properties.
The curd cannot be turned back into milk: the change is irreversible.

Answer: Chemical

Memory hook: New taste and texture means a new substance.

Dissolving

Imagine you stir 15 g of sugar into 200 g of tea.

What mass of sweet tea do you have, and what kind of change is this?

Try it first, then show the solutionSolution

Mass is conserved: $15 + 200 = 215$ g.
The sugar is still sugar (the tea tastes sweet) and could be recovered: physical change.

Answer: 215 g; physical

Memory hook: Dissolving hides a substance but does not change it.

Rusting

Suppose an iron gate left in the rain develops a flaky brown coating.

Why is this a chemical change, and how could it be slowed?

Try it first, then show the solutionSolution

Rust is a new brown substance formed from iron, oxygen and water; it has different properties from iron.
Painting or oiling the gate keeps out air and water and slows rusting.

Answer: Chemical; paint or oil the iron

Memory hook: Rust is a new substance, not just dirty iron.

Topics in this chapter

Physical and Chemical Changes formula sheet

Burning magnesium: $2 M g + O_{2} \to 2 M g O$; Chemical change: bright light, new white powder.
Iron and copper sulphate: $F e + C u S O_{4} \to F e S O_{4} + C u$; Blue to green; brown copper deposit.
Quicklime and water: $C a O + H_{2} O \to C a (O H)_{2}$; Gives out a lot of heat.

Physical and Chemical Changes: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

Iron nail in copper sulphate solution

Draw an experiment that shows a chemical change.

Draw

Two test tubes in a stand.
Tube A: blue copper sulphate solution with a clean iron nail hanging in it, at the start.
Tube B: the same after 30 minutes, with green solution and a brown coating on the nail.

Label

Copper sulphate solution (blue)
Iron nail
Iron sulphate solution (green)
Brown copper coating

Watch out: Label the colours before and after; they are the evidence of a new substance.

How the school exam asks Physical and Chemical Changes

The question patterns to expect, and the method that works for each.

Question type	How it is asked	Method
Definitions	Define physical change and chemical change with one example each.	New substance or not; reversible or not.
Differences	Give three differences between physical and chemical changes.	Use the table: new substance, composition, reversibility, energy.
Classify	Classify given changes (rusting, melting butter, curdling milk) with reasons.	Ask 'is a new substance formed?' first.
Signs of a chemical change	What observations show that a chemical change has taken place?	Colour, gas, precipitate, heat/light, smell.
Mixed changes	Which changes happen when a candle burns?	Separate the physical and chemical parts.

Tricks to remember Physical and Chemical Changes

Short memory aids. Say each one aloud once, then use it on a question the same day.

New stuff = chemical
If a new substance appears, it is chemical; if not, it is physical.
Use it when: Any classification.
CGPHS
Colour, Gas, Precipitate, Heat/light, Smell: the five signs of a chemical change.
Use it when: Observation questions.
State change is physical
Melting, freezing, boiling, condensing and sublimation are all physical.
Use it when: Change of state examples.
Candle = both
A candle melts (physical) and burns (chemical) at the same time.
Use it when: Mixed-change questions.

Physical and Chemical Changes: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Example 1: Pick the chemical change · 1 mark · MCQExam level

Which of these is a chemical change?
(a) melting of wax
(b) dissolving salt in water
(c) rusting of iron
(d) breaking a glass

Try it first, then show the solutionSolution

(a), (b) and (d) form no new substance.
Rusting forms a new brown substance.

Answer: (c)

Example 2: Two definitions · 2 marks · Short answerExam level

Define a physical change and a chemical change, with one example of each.

Try it first, then show the solutionSolution

Physical change: only physical properties change; no new substance is formed (e.g. melting of ice).
Chemical change: one or more new substances with new properties are formed (e.g. burning of paper).

Answer: As above

Example 3: Three differences · 3 marks · Short answerExam level

Give three differences between a physical change and a chemical change.

Try it first, then show the solutionSolution

Physical: no new substance; chemical: new substance formed.
Physical: usually reversible; chemical: usually irreversible.
Physical: little energy change; chemical: heat or light is usually given out or taken in.

Answer: As above

Example 4: Classify with reasons · 3 marks · Short answerHarder exam level

Classify as physical or chemical, giving a reason: (i) formation of dew (ii) cooking an egg (iii) magnetising an iron nail.

Try it first, then show the solutionSolution

(i) Physical: water vapour condenses; no new substance.
(ii) Chemical: the egg changes permanently; new substances form.
(iii) Physical: the nail is still iron and can lose its magnetism.

Answer: (i) Physical (ii) Chemical (iii) Physical

Example 5: Quicklime and water · 3 marks · Short answerHarder exam level

Water is poured on quicklime (calcium oxide). It hisses and becomes very hot. What kind of change is this? Give two observations that support your answer and write the equation.

Try it first, then show the solutionSolution

A lot of heat is produced, with a hissing sound.
A new substance, slaked lime (calcium hydroxide), is formed.
Chemical change: $C a O + H_{2} O \to C a (O H)_{2}$ .

Answer: Chemical change

Example 6: The burning candle · 4 marks · Long answerHarder exam level

Explain why burning a candle involves both a physical change and a chemical change. Which part can be reversed?

Try it first, then show the solutionSolution

Near the flame the solid wax melts and some turns into vapour: physical changes of state.
The wax vapour burns in oxygen, giving carbon dioxide, water vapour, heat and light: a chemical change.
The melted wax that drips down solidifies again: the physical change is reversible.
The burnt wax cannot be recovered: the chemical change is irreversible.

Answer: Melting is physical (reversible); burning is chemical (irreversible).

Example 7: Is it really chemical? · 4 marks · Long answerHOTS / competency

A student says: 'When water boils, a gas is given off, so boiling is a chemical change.' Another says: 'Breaking a cup is irreversible, so it is chemical.' Correct both students.

Try it first, then show the solutionSolution

Boiling: the gas is steam, which is still water; no new substance forms.
Steam condenses back to water, so boiling is physical.
Breaking a cup: the pieces are still the same material; only the shape changes.
It is irreversible but physical: the test is whether a new substance forms, not whether it can be undone.

Answer: Both are physical changes; the key test is a new substance.

Case-study practice (Section B style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 8-mark question split into 2 + 3 + 3 marks.

A kitchen investigation

Suppose Riya records changes in her kitchen: (A) butter melting in a pan, (B) bread being toasted brown, (C) sugar dissolving in tea, (D) a cut apple turning brown, (E) water vapour from a kettle forming drops on a cold tile.

(i) · 2 marks
Classify each change as physical or chemical.
Answer
Answer: A, C, E physical; B, D chemical
Melting, dissolving and condensing form no new substance. Toasting and the browning of the apple form new substances.
(ii) · 3 marks
Give one observation for each chemical change that shows a new substance has formed.
Answer
Answer: Colour and smell changes
Toast: the bread turns brown and smells different. Cut apple: the surface turns brown on standing in air.
(iii) · 3 marks
Which of A, C and E can be reversed, and how?
Answer
Answer: All three
A: cool the butter to solidify it. C: evaporate the tea to leave the sugar (with other solids). E: heat the drops to turn them back into vapour.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Why is the melting of ice a physical change? (2 marks)

Step	Marks
No new substance forms: ice and water are both water	1
It is reversible: water can be frozen back into ice	1

State three signs that show a chemical change has taken place, with an example of each. (3 marks)

Step	Marks
Change of colour (iron in copper sulphate: blue to green)	1
Gas given off (baking soda and vinegar fizz)	1
Heat or light produced (burning magnesium)	1

A strip of zinc is kept in blue copper sulphate solution. State two observations, the type of change, and the equation. (4 marks)

Step	Marks
The blue colour of the solution fades and it becomes colourless	1
A reddish-brown coating of copper forms on the zinc	1
Chemical change: new substances (zinc sulphate and copper) form	1
$Z n + C u S O_{4} \to Z n S O_{4} + C u$	1

Where students lose marks in Physical and Chemical Changes

The slips examiners see most often, and what to write instead.

Mistake: Using 'irreversible' as the only test
Some physical changes (breaking glass) cannot easily be reversed.
Do this: Test for a new substance first.
Usually costs: 1 mark.
Mistake: Calling dissolving a chemical change
The dissolved substance is unchanged and can be recovered.
Do this: Dissolving is physical.
Usually costs: 1 mark.
Mistake: Classifying without a reason
Most questions ask 'give a reason'.
Do this: Add 'because no new substance forms' or 'because a new substance forms'.
Usually costs: 1 mark per item.
Mistake: Saying a bulb filament glowing is chemical
The filament is unchanged and stops glowing when switched off.
Do this: Glowing of a filament is physical.
Usually costs: 1 mark.
Mistake: Unbalanced or wrong equations
Equations must show the correct new substances and be balanced.
Do this: Check formulae and count atoms.
Usually costs: 1 mark.

Practice questions on Physical and Chemical Changes

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQExam level
Which of these is a physical change?
(a) burning wood
(b) curdling of milk
(c) melting of ice
(d) rusting of iron
Hint
No new substance.
Answer
(c)
Q2 · 1 mark · Very short answerExam level
Is the formation of clouds a physical or chemical change?
Hint
Condensation.
Answer
Physical.
Q3 · 2 marks · Short answerExam level
Give two examples each of physical and chemical changes from daily life.
Hint
Kitchen and outdoors.
Answer
Physical: melting butter, drying clothes. Chemical: cooking food, rusting of iron.
Q4 · 2 marks · Short answerHarder exam level
Why is the ripening of fruit a chemical change?
Hint
Taste and colour.
Answer
New substances form: the fruit's colour, taste and smell change, and the change cannot be reversed.
Q5 · 1 mark · Assertion-reasonHarder exam level
Assertion (A): Dissolving salt in water is a physical change.
Reason (R): The salt can be recovered by evaporating the water.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation for (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation for (A).
Hint
No new substance; reversible.
Answer
(c)
Q6 · 2 marks · Short answerHarder exam level
Classify, with reasons: (i) stretching a rubber band (ii) burning a matchstick.
Hint
New substance?
Answer
(i) Physical: only the shape changes and it returns. (ii) Chemical: new substances (ash, gases) with heat and light.
Q7 · 3 marks · Short answerHarder exam level
Baking soda is added to vinegar and it fizzes. State the type of change and two observations that support it.
Hint
Gas.
Answer
Chemical change: bubbles of a gas (carbon dioxide) are given off, and the mixture feels slightly cold as the reaction takes in heat; new substances form.
Q8 · 2 marks · Short answerHarder exam level
50 g of ice melts completely. What mass of water is formed, and what does this show?
Hint
Conservation.
Answer
50 g. Mass does not change in a physical change; only the state changes.
Q9 · 3 marks · Short answerHarder exam level
Explain why heating sugar strongly until it turns black is a chemical change, but heating it gently until it melts is a physical change.
Hint
What is left?
Answer
Gentle heating only melts sugar, which solidifies back into sugar: physical. Strong heating forms a black substance (mainly carbon) and gives off water vapour; the sugar cannot be recovered: chemical.
Q10 · 3 marks · Short answerHarder exam level
Write the balanced equation for burning magnesium and state two observations.
Hint
Bright light.
Answer
$2 M g + O_{2} \to 2 M g O$ . It burns with a dazzling white light, leaving a white powder (magnesium oxide).
Q11 · 3 marks · Short answerHOTS / competency
Carbon dioxide is bubbled through clear lime water, and it turns milky. Is this a physical or a chemical change? Explain, and write the equation.
Hint
What makes it milky?
Answer
Chemical: the milkiness is a new insoluble white substance, calcium carbonate, formed by the reaction $C a (O H)_{2} + C O_{2} \to C a C O_{3} + H_{2} O$ .
Q12 · 3 marks · Short answerHOTS / competency
Explain why a firework display involves chemical changes, mentioning at least two signs.
Hint
Light, sound, gases.
Answer
The chemicals in the firework burn to form new substances (smoke and gases), giving out heat, bright coloured light and sound. These signs show chemical changes, and the firework cannot be restored.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Is rusting physical or chemical?Show answer
Chemical.
2.Is melting of wax physical or chemical?Show answer
Physical.
3.Give one sign of a chemical change.Show answer
Change of colour (or gas evolved, precipitate, heat/light, smell).
4.Is curdling of milk reversible?Show answer
No.
5.Name the product when magnesium burns.Show answer
Magnesium oxide.
6.What colour does copper sulphate solution turn when iron is added?Show answer
Green.
7.Is digestion physical or chemical?Show answer
Chemical.
8.Is the total mass conserved in a chemical change?Show answer
Yes.

Best order to study it

Revise the definitions of physical and chemical changes.
Learn the table of differences.
Learn the signs of a chemical change with examples.
Practise classifying everyday changes with reasons.
Finish with mixed changes (candle) and equations.

Quick revision checklist

The night before the exam: can you do each of these without looking?

Did you ask whether a new substance forms?
Can you give three differences between the two kinds of change?
Can you list five signs of a chemical change?
Can you classify twelve everyday changes with reasons?
Can you explain the burning candle?
Are your equations balanced?

Physical and Chemical Changes: frequently asked questions

Is dissolving sugar a chemical change because the sugar disappears?

No. The sugar is still there, spread through the water; the solution tastes sweet and the sugar can be recovered by evaporation.

Are all chemical changes irreversible?

Most everyday chemical changes are, but some can be reversed by another chemical reaction. The key test is that a new substance forms.

Why is a change of state a physical change?

The substance stays the same; only the arrangement and movement of its particles change.

Is photosynthesis a chemical change?

Yes. Carbon dioxide and water are turned into glucose and oxygen, which are new substances.

Does mass change in a chemical change?

The total mass stays the same (law of conservation of mass), even though the substances change.

Based on: CISCE Curriculum for Upper Primary Classes (VI-VIII), Science: Chemistry (Class VIII); CISCE RDCD: Curriculum Pre-School to Class VIII