PhysicsICSE Class 8 · Matter

States of Matter and Change of State: Melting, Boiling, Sublimation and Deposition (ICSE Class 8)

Updated 17 October 2026 · Fact-checked

Matter exists as solid, liquid or gas. On heating, a solid melts to a liquid, a liquid boils to a gas, and some solids sublime directly to a gas; cooling reverses these changes (freezing, condensation, deposition). Each is a physical change, and a pure substance changes state at a fixed temperature.

Understand States of Matter and Change of State

Matter is anything that has mass and occupies space. Its three common states differ in shape, volume and particle arrangement.

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

Heating gives the particles more energy, so they move faster and overcome the forces holding them together (solid to liquid to gas). Cooling takes energy away, so they slow down and come closer (gas to liquid to solid).

The six changes.

Melting: solid → liquid on heating at the melting point (ice: 0 °C).
Freezing: liquid → solid on cooling. For a pure substance the freezing point equals the melting point.
Boiling (vaporisation): liquid → gas on heating at the boiling point (pure water: 100 °C at normal pressure); bubbles form throughout the liquid.
Condensation: gas → liquid on cooling (dew, mist on a cold glass, steam on a lid).
Sublimation: solid → gas directly, with no liquid stage: naphthalene balls, camphor, iodine, ammonium chloride, dry ice.
Deposition: gas → solid directly: frost on a very cold night, iodine vapour forming crystals on a cold surface.

The state diagram. Put solid, liquid and gas at the corners of a triangle: solid ⇄ liquid (melting, freezing); liquid ⇄ gas (boiling, condensation); solid ⇄ gas (sublimation, deposition). Arrows towards a "freer" state need heating; the reverse need cooling.

During a change of state the temperature stays constant even while heat is supplied: the heat is used to free particles, not to speed them up. This hidden heat is called latent heat.

Physical, not chemical. Ice, water and steam are all water. The substance is the same and the change can be reversed, so these are physical changes.

States of Matter and Change of State: formulas and key facts

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

How to solve States of Matter and Change of State questions

To name a change, find the starting and ending states, then ask whether heat is added or removed.

1Write the initial and final states.
2Match the pair to the diagram: solid-liquid, liquid-gas or solid-gas.
3If the direction is towards the freer state, heat is taken in; otherwise it is given out.
4For sublimation and deposition, check that no liquid appears.

States of Matter and Change of State in real life

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.

Vanishing naphthalene

Suppose naphthalene balls in a cupboard get smaller every month, leave no wet patch, and the cupboard smells of them.

Name the change and explain why no liquid appears.

Try it first, then show the solutionSolution

The solid changes directly into vapour: sublimation.
The vapour spreads through the cupboard, which is why you smell it.

Answer: Sublimation: solid to gas without passing through a liquid.

Memory hook: Solid to gas, skipping liquid.

Dew on a cold glass

Imagine a glass of cold water is left on a table on a humid day and drops form on its outside.

Name the change.

Try it first, then show the solutionSolution

Water vapour in the air touches the cold glass and loses energy.
It changes to liquid droplets: condensation.

Answer: Condensation.

Memory hook: Cool vapour turns to drops.

Tricks to remember States of Matter and Change of State

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

Triangle of states
Solid at the base left, liquid at the top, gas at the base right: three pairs, six names.
Use it when: Change diagram.
Skip the liquid
Sublimation and deposition skip the liquid state.
Use it when: Direct changes.
Heat up the arrow
Towards gas needs heat, towards solid needs cooling.
Use it when: Direction.

States of Matter and Change of State: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Sublimation · 1 mark · MCQBoard level

Which of the following is an example of sublimation?
(a) Ice becoming water
(b) Naphthalene ball becoming vapour without liquid
(c) Steam becoming water
(d) Water becoming ice

Try it first, then show the solutionSolution

In sublimation a solid changes directly into a gas, as camphor and naphthalene do.

Answer: (b)

Example 2: Name the change · 2 marks · Short answerBoard level

Name the change of state in each: (a) water to steam at 100 °C, (b) steam to water on a cold lid, (c) ice to water at 0 °C, (d) iodine vapour to iodine crystals on a cold surface.

Try it first, then show the solutionSolution

(a) Boiling (vaporisation); (b) condensation; (c) melting; (d) deposition. (½ each)

Answer: (a) boiling (b) condensation (c) melting (d) deposition

Example 3: Three states · 3 marks · Short answerHarder board level

Compare solids, liquids and gases in terms of (a) shape, (b) volume, (c) arrangement and movement of particles.

Try it first, then show the solutionSolution

(a) Solid: fixed shape; liquid: takes the container shape; gas: fills the container. (1)
(b) Solid and liquid have fixed volume; gas has none. (1)
(c) Solid: closely packed and vibrating in place; liquid: close but sliding past one another; gas: far apart and moving freely and fast. (1)

Answer: See the working.

Example 4: The constant temperature · 3 marks · Short answerHarder board level

A beaker of crushed ice is heated steadily and stirred. Why does the thermometer read 0 °C until all the ice has melted, although heat is supplied? What is the relation between the melting point of a pure solid and the freezing point of the liquid?

Try it first, then show the solutionSolution

The heat supplied is used to free the particles from their fixed positions, not to raise the temperature. (1½)
The temperature rises only after the ice has melted. (½)
For a pure substance the melting point equals the freezing point (0 °C for water). (1)

Answer: Heat is used to change state; melting point equals freezing point.

Example 5: The camphor experiment · 4 marks · Case-basedHOTS / competency

A mixture of camphor and sand is heated in a china dish covered by an inverted funnel with a cotton plug. (a) Name the change in the dish. (b) Name the change on the cold funnel wall. (c) Why is no liquid camphor seen? (d) What remains in the dish?

Try it first, then show the solutionSolution

(a) Sublimation: solid camphor changes to vapour. (1)
(b) Deposition: camphor vapour changes to solid on the cold wall. (1)
(c) Camphor goes directly from solid to gas and back to solid, so a liquid never forms. (1)
(d) Sand. (1)

Answer: (a) sublimation (b) deposition (c) no liquid stage (d) sand

Where students lose marks in States of Matter and Change of State

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

Mistake: Calling sublimation "melting then boiling"
There is no liquid stage in sublimation.
Wrong working
"Camphor melts and then vaporises."
Right working
"Camphor sublimes: solid directly to gas."
Do this: Check for a liquid.
Mistake: Mixing up condensation and freezing
Condensation is gas to liquid.
Wrong working
"Steam to water is freezing."
Right working
"Steam to water is condensation."
Do this: Name the states before naming the change.
Mistake: Saying the temperature rises during melting
It stays constant.
Wrong working
"The temperature increases as ice melts."
Right working
"The temperature stays at 0 °C until all ice has melted."
Do this: Learn the flat part.

Exam tips

Name the change from the start and end states, then state if heat is taken in or given out.
Give two examples for each change when asked.
Use "physical change" with a reason: no new substance, reversible.
Draw the triangle with all six names if the question says "diagram".

Practice questions on States of Matter and Change of State

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 · Very short answerBoard level
Frost appears on a window pane on a very cold night. Name the change of state that produces it.
Hint
Gas straight to solid.
Answer
Deposition: water vapour changes directly into ice crystals.
Q2 · 3 marks · Short answerHarder board level
Draw the change-of-state triangle in words: list the six changes with the direction of energy flow.
Hint
Heating moves towards the gas corner.
Answer
Solid to liquid: melting (heat taken in). Liquid to solid: freezing (heat given out). Liquid to gas: boiling (heat taken in). Gas to liquid: condensation (heat given out). Solid to gas: sublimation (heat taken in). Gas to solid: deposition (heat given out).
Q3 · 2 marks · Short answerHarder board level
Ice, water and steam are three forms of the same substance. Is the change from one to another physical or chemical? Give two reasons.
Hint
Is a new substance formed?
Answer
Physical. No new substance is formed (all are water), and the change can be reversed by heating or cooling.
Q4 · 3 marks · Short answerHarder board level
Using the idea of particles, explain why a gas fills its container but a liquid does not.
Hint
Space and attraction.
Answer
In a gas the particles are far apart with very weak attraction and move freely in all directions, so they spread to fill all the space. In a liquid they are close and attract each other enough to stay together, giving a fixed volume with the shape of the container.
Q5 · 4 marks · Long answerHOTS / competency
A student says: "Naphthalene balls melt and then evaporate; dry ice also melts." Correct the statement using the terms of the chapter, and give one evidence for each.
Hint
Is there a wet patch?
Answer
Naphthalene and dry ice sublime: they change from solid to gas without a liquid stage. Evidence: the naphthalene balls shrink and leave no liquid, with a smell from the vapour; dry ice leaves no puddle. The reverse change of vapour to solid is deposition.

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.Melting point of ice?Show answer
0 °C.
2.Boiling point of pure water?Show answer
100 °C at normal pressure.
3.Solid to gas directly?Show answer
Sublimation.
4.Gas to solid directly?Show answer
Deposition.
5.Is change of state physical or chemical?Show answer
Physical.

States of Matter and Change of State: frequently asked questions

What is sublimation?

Sublimation is the change of a solid directly into a gas on heating, without becoming a liquid. Naphthalene, camphor, iodine, ammonium chloride and dry ice sublime.

Why does the temperature stay constant during melting?

The heat supplied is used to separate particles from their fixed positions, not to make them move faster, so the temperature stays constant until the change of state is complete.

What are the six changes of state?

Melting, freezing, boiling, condensation, sublimation and deposition.