PhysicsICSE Class 8 · Chapter 1

Matter ICSE Class 8 Physics: Change of State, Sublimation and Deposition

Updated 15 October 2026 · Fact-checked

Matter changes state when it is heated or cooled. In ICSE Class 8, melting and freezing link solid and liquid, boiling and condensation link liquid and gas, and sublimation and deposition link solid and gas directly. A pure substance melts and boils at fixed temperatures, which stay constant until the change is complete.

What Matter is about

Matter is anything that has mass and takes up space. It exists in three common states: solid, liquid and gas. The same substance can be found in all three: ice, water and steam.

The CISCE Class VIII curriculum asks you to understand change of state:

melting and freezing (solid ⇄ liquid),
boiling and condensation (liquid ⇄ gas),
sublimation and deposition (solid ⇄ gas, skipping the liquid state),
the change of state diagram that links all six terms,
interconversion of states with examples such as water and naphthalene balls,
change of state by heating or cooling,
the fact that a pure substance melts or boils at a fixed temperature.

A change of state is a physical change: the substance stays the same (ice, water and steam are all water), and the change can be reversed by reversing the heating or cooling. You will also read simple heating and cooling curves (temperature–time graphs) and explain the flat parts.

Weightage: CISCE publishes no question paper, marking scheme or chapter weightage for Class VIII Physics: your school sets and marks the exam. Matter sits in the Theme 1: Matter theme of the CISCE Curriculum for Upper Primary Classes (VI-VIII).Source: CISCE Curriculum for Upper Primary Classes (VI-VIII), RDCD 2016

Key concepts

The three states and heating or cooling

Property	Solid	Liquid	Gas
Shape	fixed	takes the shape of the container	fills the whole container
Volume	fixed	fixed	not fixed
Particles	closely packed, vibrate in place	close, but can slide past each other	far apart, move freely and fast

Heating gives the particles more energy, so they move faster and can overcome the forces holding them together: solid → liquid → gas.

Cooling takes energy away, so the particles slow down and come closer: gas → liquid → solid.

Worked example

Why does an ice cube placed on a plate turn into water, and how can the water be turned back into ice?

Try it first, then show the solutionSolution

Heat from the warmer room is taken in by the ice; its particles gain energy and break out of their fixed positions: the ice melts.
Putting the water in a freezer removes heat; the particles slow down and lock into place: the water freezes.

Answer: Heating melts it; cooling freezes it again (a reversible change).

Melting and freezing

Melting (fusion): solid → liquid on heating. The fixed temperature at which a pure solid melts is its melting point. Ice melts at $0 ° C$ .
Freezing (solidification): liquid → solid on cooling. For a pure substance the freezing point equals the melting point: water freezes at $0 ° C$ .

While melting, the temperature stays constant even though heat is still being supplied. The heat is used to free the particles from their fixed positions rather than to raise the temperature. (This hidden heat is called latent heat.)

Worked example

A mixture of ice and water is heated and stirred. What does a thermometer in it show until all the ice has melted?

Try it first, then show the solutionSolution

The ice is melting, and melting happens at a fixed temperature.
The heat supplied is used to melt the ice, not to raise the temperature.

Answer: It stays at $0 ° C$ until all the ice has melted.

Boiling and condensation

Boiling: liquid → gas on heating, at a fixed temperature called the boiling point. Bubbles of vapour form throughout the liquid. Pure water boils at $100 ° C$ at normal atmospheric pressure.
Condensation: gas (vapour) → liquid on cooling. Water vapour condenses on a cold glass of water, on a bathroom mirror, or as dew.

During boiling, too, the temperature stays constant until all the liquid has changed into vapour.

The change from liquid to gas is also called vaporisation; it can happen by boiling or by evaporation (studied in Heat Transfer).

Worked example

Water is boiling in an open pan on a stove at normal atmospheric pressure. If the flame is turned up, what happens to the temperature of the water?

Try it first, then show the solutionSolution

Boiling takes place at a fixed temperature, $100 ° C$ here.
Extra heat makes the water boil away faster, but the temperature does not rise.

Answer: It stays at $100 ° C$ ; the water simply boils away faster.

Sublimation and deposition

Sublimation: a solid changes directly into a gas on heating, without becoming a liquid. Examples: naphthalene balls, camphor, iodine, ammonium chloride, dry ice (solid carbon dioxide).
Deposition: a gas changes directly into a solid on cooling. Examples: frost forming from water vapour on a very cold night; iodine vapour forming crystals on a cold surface.

Naphthalene balls kept in a cupboard slowly get smaller and leave no liquid behind: they sublime, and the smell in the cupboard is the vapour.

Worked example

A block of camphor of mass 12 g is left in an open dish. After 5 weeks its mass is 9 g, and no liquid is seen. Name the change and find the average loss of mass per week.

Try it first, then show the solutionSolution

Solid → gas directly with no liquid: sublimation.
Mass lost $= 12 - 9 = 3$ g in 5 weeks.
Average $= 3 \div 5 = 0.6$ g per week.

Answer: Sublimation; 0.6 g per week

The change of state diagram

Place solid, liquid and gas at the corners of a triangle and join them with pairs of arrows:

solid → liquid: melting; liquid → solid: freezing;
liquid → gas: boiling (vaporisation); gas → liquid: condensation;
solid → gas: sublimation; gas → solid: deposition.

Arrows that point towards a 'freer' state (solid → liquid → gas) need heating; arrows the other way need cooling.

Worked example

In the change of state diagram, which three changes need cooling?

Try it first, then show the solutionSolution

Cooling makes particles come closer: changes towards the solid state.
Gas → liquid (condensation), liquid → solid (freezing), gas → solid (deposition).

Answer: Condensation, freezing and deposition

Heating and cooling curves

Heat ice steadily from $- 10 ° C$ and record the temperature each minute. The temperature–time graph:
1. rises (ice warming) to $0 ° C$ ;
2. is flat at $0 ° C$ (melting: ice and water together);
3. rises (water warming) to $100 ° C$ ;
4. is flat at $100 ° C$ (boiling: water and steam together).

The flat parts show a change of state at a fixed temperature. A cooling curve is the mirror image: its flat parts show condensation and freezing. A substance that melts over a range of temperatures, instead of at one fixed temperature, is not pure.

Worked example

On a heating curve for ice, the temperature reaches $0 ° C$ at 3 min and starts rising again at 7 min; it reaches $100 ° C$ at 15 min. How long does melting take, and what is the temperature at 6 min?

Try it first, then show the solutionSolution

Melting is the flat part from 3 min to 7 min: 4 minutes.
At 6 min the ice is still melting, so the temperature is $0 ° C$ .

Answer: 4 minutes; $0 ° C$

Physics in real life: Matter

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.

Sublimation

Suppose you put a 20 g naphthalene ball in your cupboard, and after 6 weeks it weighs 14 g with no wet patch.

What happened to it, and roughly how many more weeks will the rest last at the same rate?

Try it first, then show the solutionSolution

It sublimed: solid naphthalene turned directly into vapour, which you can smell.
Rate $= 6 \div 6 = 1$ g per week, so 14 g lasts about 14 more weeks.

Answer: Sublimation; about 14 more weeks

Memory hook: No puddle means it skipped the liquid state.

Condensation

Imagine you take a cold bottle out of the fridge on a humid day and drops form on the outside.

Where does the water come from?

Try it first, then show the solutionSolution

Water vapour in the air touches the cold surface and is cooled.
It condenses (gas → liquid) into drops on the bottle.

Answer: From water vapour in the air, by condensation

Memory hook: Cold surfaces catch vapour as drops.

Fixed boiling point

Suppose you are boiling eggs and turn the gas up high once the water is already boiling.

Do the eggs cook faster because the water gets hotter?

Try it first, then show the solutionSolution

Boiling water stays at its boiling point (about $100 ° C$ in an open pan at normal pressure).
Extra heat only boils the water away faster; the temperature does not rise.

Answer: No; it only wastes fuel and water

Memory hook: Boiling point is a fixed temperature.

Topics in this chapter

Matter formula sheet

Solid and liquid: $solid melting liquid freezing solid$; Melting point = freezing point (pure substance).
Liquid and gas: $liquid boiling gas condensation liquid$; Water boils at 100 °C at normal pressure.
Solid and gas directly: $solid sublimation gas deposition solid$; Naphthalene, camphor, iodine.

Matter: diagrams to practise

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

Change of state diagram

Draw and label the change of state diagram using the terms melting, freezing, boiling, condensation, sublimation and deposition.

Draw

A triangle with SOLID at the bottom left, LIQUID at the bottom right and GAS at the top.
Two arrows between each pair of states, pointing in opposite directions.
Write 'heat' beside the arrows going towards gas and 'cool' beside the arrows going towards solid.

Label

Melting (solid → liquid)
Freezing (liquid → solid)
Boiling (liquid → gas)
Condensation (gas → liquid)
Sublimation (solid → gas)
Deposition (gas → solid)

Watch out: Check that each arrow carries the right name; examiners often check sublimation and deposition in particular.

Heating curve of ice

Draw the temperature–time graph when ice at −10 °C is heated until the water boils, and explain the flat parts.

Draw

Axes: time (min) horizontally, temperature (°C) vertically, with 0 °C and 100 °C marked.
A rising line from −10 °C to 0 °C.
A flat line at 0 °C, then a rising line to 100 °C, then a flat line at 100 °C.

Label

Ice warming
Melting (ice + water) at 0 °C
Water warming
Boiling (water + steam) at 100 °C

Watch out: Label the two flat parts with the change of state happening there.

How the school exam asks Matter

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

Question type	How it is asked	Method
Name the change	Name the change of state: frost on a window; naphthalene balls shrinking; dew on grass.	Identify the starting and final states, then use the diagram.
Diagram	Draw the change of state diagram using six given terms.	Triangle of states with labelled pairs of arrows.
Fixed temperature	Why does the temperature not rise while ice melts?	Heat is used to change the state, not to raise the temperature.
Graphs	Read a heating or cooling curve: melting point, time taken to melt.	Flat parts are changes of state; read their temperature and length.
Examples	Give two examples of substances that sublime; one example of deposition.	Naphthalene, camphor, iodine, dry ice; frost.

Tricks to remember Matter

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

Heat climbs, cold falls
Heating moves matter up the ladder solid → liquid → gas; cooling moves it down.
Use it when: Deciding whether a change needs heating or cooling.
Sublime skips
Sublimation skips the liquid on the way up; deposition skips it on the way down.
Use it when: Solid ⇄ gas changes.
Flat line = state change
On a temperature–time graph, every flat line is a change of state.
Use it when: Reading heating and cooling curves.
Melt = freeze point
A pure substance melts and freezes at the same temperature (0 °C for water).
Use it when: Fixed-point questions.

Matter: exam-level solved questions

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

Example 1: Name the change · 1 mark · MCQExam level

Frost forming on a car window on a very cold night is an example of:
(a) condensation
(b) freezing
(c) deposition
(d) sublimation

Try it first, then show the solutionSolution

Water vapour in the air turns directly into ice crystals.
Gas → solid directly is deposition.

Answer: (c)

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

Define sublimation and deposition, giving one example of each.

Try it first, then show the solutionSolution

Sublimation: change of a solid directly into a gas on heating, e.g. naphthalene balls or camphor.
Deposition: change of a gas directly into a solid on cooling, e.g. frost forming from water vapour.

Answer: As above

Example 3: Why the temperature stays constant · 3 marks · Short answerExam level

Ice at $0 ° C$ is heated steadily. Explain why its temperature does not rise until all the ice has melted.

Try it first, then show the solutionSolution

Melting happens at a fixed temperature, the melting point ( $0 ° C$ ).
The heat supplied is used to overcome the forces holding the particles in place.
Only after all the ice has melted does the heat start to raise the temperature.

Answer: The heat is used to change the state, not to raise the temperature.

Example 4: Reading a heating curve · 3 marks · Short answerHarder exam level

Ice at $- 10 ° C$ is heated steadily. The temperature reaches $0 ° C$ at 2 min, stays there until 8 min, rises to $100 ° C$ at 18 min and stays there until 30 min. (i) How long does melting take? (ii) How long does boiling last? (iii) What is present at 25 min?

Try it first, then show the solutionSolution

(i) Flat at $0 ° C$ from 2 to 8 min: 6 min.
(ii) Flat at $100 ° C$ from 18 to 30 min: 12 min.
(iii) At 25 min it is boiling: water and steam together.

Answer: (i) 6 min (ii) 12 min (iii) water and steam

Example 5: The change of state diagram · 4 marks · Long answerHarder exam level

Draw a labelled change of state diagram using the terms melting, freezing, boiling, condensation, sublimation and deposition. Mark which changes need heating.

Try it first, then show the solutionSolution

Draw a triangle with solid, liquid and gas at its corners.
Solid ⇄ liquid: melting (→) and freezing (←); liquid ⇄ gas: boiling and condensation.
Solid ⇄ gas: sublimation and deposition.
Heating: melting, boiling, sublimation; cooling: freezing, condensation, deposition.

Answer: Diagram as described; heating for melting, boiling and sublimation

Example 6: A cooling curve · 4 marks · Long answerHarder exam level

A hot liquid is left to cool and its temperature is read every minute: 90, 80, 72, 72, 72, 72, 65, 58 °C. (i) What is its freezing point? (ii) How long does freezing take? (iii) What would you expect its melting point to be? Explain.

Try it first, then show the solutionSolution

(i) The temperature stays constant at $72 ° C$ : freezing point $72 ° C$ .
(ii) It stays at 72 from the 2nd to the 5th minute: 3 minutes.
(iii) For a pure substance the melting point equals the freezing point.
So the melting point should be $72 ° C$ .

Answer: (i) 72 °C (ii) 3 min (iii) 72 °C

Example 7: Separating a mixture by sublimation · 4 marks · Long answerHOTS / competency

A student has a mixture of common salt and ammonium chloride. Ammonium chloride sublimes; salt does not. Explain how the two can be separated, naming the changes of state involved, and say where the ammonium chloride is collected.

Try it first, then show the solutionSolution

Heat the mixture in a china dish covered by an inverted funnel with its stem plugged with cotton.
Ammonium chloride sublimes (solid → gas); salt is left behind in the dish.
The vapour meets the cool inner surface of the funnel and deposits (gas → solid) as a solid.
So ammonium chloride is collected on the inside of the funnel, and salt remains in the dish.

Answer: Sublimation then deposition; ammonium chloride collects on the funnel, salt stays in the dish.

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.

The water cycle in a kitchen

Suppose Riya heats a pan of water with a lid. Drops form under the lid and fall back. Later she puts a tray of water in the freezer, and one cold morning she sees frost on the grass outside.

(i) · 2 marks
Name the change of state when the water boils and when drops form under the lid.
Answer
Answer: Boiling; condensation
Liquid → gas is boiling; the steam meets the cooler lid and turns back into liquid: condensation.
(ii) · 3 marks
In the freezer, the water's temperature falls to $0 ° C$ and then stays there for a while. Explain why.
Answer
Answer: It is freezing at a fixed temperature
At its freezing point water changes from liquid to solid. While this happens, heat is removed without the temperature falling, until all the water has frozen.
(iii) · 3 marks
Frost forms on the grass without any dew forming first. Name this change and state whether heat is given out or taken in by the vapour.
Answer
Answer: Deposition; heat is given out
Water vapour changes directly into ice: deposition. It is a cooling change, so the vapour gives out heat to the colder surroundings.

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.

State two differences between melting and sublimation. (2 marks)

Step	Marks
Melting: solid → liquid; sublimation: solid → gas directly	1
Example: ice melts; naphthalene sublimes (no liquid formed)	1

Explain why the temperature of boiling water does not rise even though it is still being heated. (3 marks)

Step	Marks
Water boils at a fixed temperature (100 °C at normal pressure)	1
The heat supplied is used to change liquid into vapour	1
So the temperature stays constant until all the water has boiled away	1

Draw the heating curve when ice at −10 °C is heated until the water boils, and label each part. (4 marks)

Step	Marks
Axes labelled: time (min) and temperature (°C)	1
Rising part to 0 °C, then flat at 0 °C labelled 'melting'	1
Rising part from 0 °C to 100 °C labelled 'water warming'	1
Flat part at 100 °C labelled 'boiling'	1

Where students lose marks in Matter

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

Mistake: Calling frost 'freezing'
Frost forms directly from vapour, not from liquid water.
Wrong working
Frost: freezing
Right working
Frost: deposition (gas → solid)
Do this: Ask: was there a liquid stage? If not, it is sublimation or deposition.
Usually costs: 1 mark.
Mistake: Saying the temperature rises during melting
Melting and boiling happen at fixed temperatures.
Do this: Say the heat is used to change the state.
Usually costs: 1 to 2 marks.
Mistake: Mixing up sublimation and deposition
They are opposite changes.
Do this: Sublimation goes up (solid → gas, needs heat); deposition comes down (gas → solid).
Usually costs: 1 mark.
Mistake: Unlabelled arrows on the change of state diagram
The marks are for the names on each arrow.
Do this: Write all six terms, one beside each arrow.
Usually costs: Up to 3 marks.
Mistake: Calling a change of state a chemical change
The substance is the same before and after (ice and water are both water).
Do this: A change of state is a physical change.
Usually costs: 1 mark.

Practice questions on Matter

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
Naphthalene balls disappearing slowly in a cupboard is an example of:
(a) melting
(b) evaporation
(c) sublimation
(d) condensation
Hint
No liquid is formed.
Answer
(c)
Q2 · 1 mark · Very short answerExam level
Name the change of state when water vapour forms drops on a cold mirror.
Hint
Gas → liquid.
Answer
Condensation.
Q3 · 2 marks · Short answerExam level
What is meant by melting point? State the melting point of ice.
Hint
Fixed temperature.
Answer
The fixed temperature at which a pure solid changes into a liquid. Ice melts at $0 ° C$ .
Q4 · 3 marks · Short answerHarder exam level
Which three changes in the change of state diagram need heating? Give one example of each.
Hint
Towards gas.
Answer
Melting (ice to water), boiling (water to steam), sublimation (camphor to vapour).
Q5 · 1 mark · Assertion-reasonHarder exam level
Assertion (A): The temperature of melting ice stays at 0 °C even though it is being heated.
Reason (R): During melting, the heat supplied is used to change the state.
(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
Where does the heat go?
Answer
(c)
Q6 · 2 marks · Short answerHarder exam level
Give two examples of deposition or sublimation that you can see in daily life, and name the change in each.
Hint
Cupboards and cold nights.
Answer
Naphthalene balls shrinking (sublimation); frost on grass on a very cold night (deposition).
Q7 · 2 marks · Short answerHarder exam level
A substance melts gradually between $60 ° C$ and $70 ° C$ instead of at one temperature. What does this suggest? Explain.
Hint
Pure substances have fixed melting points.
Answer
It is probably not pure: a pure substance melts at one fixed temperature.
Q8 · 2 marks · Short answerHarder exam level
During boiling, why do bubbles appear throughout the water and not just at the surface?
Hint
Whole liquid at boiling point.
Answer
At the boiling point the whole liquid is hot enough to change into vapour, so vapour bubbles form throughout it and rise to the surface.
Q9 · 3 marks · Short answerHarder exam level
In a heating curve for a pure solid, the temperature stays at $80 ° C$ from 4 min to 10 min. What is happening, what is the melting point, and how long does it take?
Hint
Flat part.
Answer
The solid is melting; melting point $80 ° C$ ; it takes 6 minutes.
Q10 · 3 marks · Short answerHarder exam level
Explain, in terms of particles, why heating a solid can change it into a liquid.
Hint
Energy and forces of attraction.
Answer
Heat gives the particles more energy, so they vibrate more strongly. At the melting point they overcome the forces holding them in fixed positions and can move past one another: the solid becomes a liquid.
Q11 · 3 marks · Short answerHOTS / competency
Water vapour at the top of a cold mountain forms frost directly, but on a warmer night forms dew. Explain the difference, naming each change.
Hint
Below or above 0 °C.
Answer
On the warmer night the surfaces are above $0 ° C$ , so vapour condenses to liquid drops (dew). When surfaces are well below $0 ° C$ , vapour changes directly into ice (deposition), giving frost.
Q12 · 3 marks · Short answerHOTS / competency
Iodine crystals are gently heated in a beaker covered with a dish of cold water. Purple vapour appears and crystals form on the bottom of the dish. Name the two changes and say why the dish is kept cold.
Hint
Up and down without liquid.
Answer
Sublimation (solid iodine → vapour) and deposition (vapour → solid on the dish). The cold dish takes heat from the vapour so that it turns back into solid.

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.Name the change: liquid to solid.Show answer
Freezing.
2.Name the change: gas to liquid.Show answer
Condensation.
3.Name the change: solid to gas directly.Show answer
Sublimation.
4.Name the change: gas to solid directly.Show answer
Deposition.
5.Melting point of ice?Show answer
0 °C.
6.Boiling point of pure water at normal pressure?Show answer
100 °C.
7.Give two substances that sublime.Show answer
Naphthalene and camphor (also iodine, dry ice).
8.What does a flat part of a heating curve show?Show answer
A change of state at a fixed temperature.

Best order to study it

Revise the three states and the particle picture.
Learn melting/freezing and boiling/condensation with water as the example.
Learn sublimation and deposition with naphthalene, camphor and frost.
Draw the change of state diagram from memory.
Read and draw heating and cooling curves.

Quick revision checklist

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

Can you name all six changes of state?
Can you draw the change of state diagram with every arrow labelled?
Can you explain why the temperature stays constant during melting and boiling?
Can you give two examples of sublimation and one of deposition?
Can you read the melting point and the time to melt from a graph?
Do you know that a change of state is a physical change?

Matter: frequently asked questions

Is evaporation the same as boiling?

No. Both change liquid into gas, but boiling happens at a fixed temperature throughout the liquid, while evaporation happens at any temperature from the surface only. The difference is studied in Heat Transfer.

Why are naphthalene balls used in cupboards?

They sublime slowly, giving out a vapour that keeps insects away, and they leave no liquid to stain clothes.

Is the melting point always equal to the freezing point?

For a pure substance, yes. Water melts and freezes at 0 °C.

Where does the heat go while ice is melting?

It is used to break the particles out of their fixed positions in the solid, so the temperature does not rise until all the ice has melted.

Is a change of state reversible?

Yes. Reversing the heating or cooling reverses the change: water can be frozen into ice and the ice melted again.

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