KS3 · Chemistry

Changes of state: energy and evaporation

A puddle on the playground vanishes by the afternoon, yet it never got anywhere near 100 °C. It never boiled. So where did the water go? Follow the energy.

Turn the energy up. Then turn it down.

Solid

Particle energy: 0. State: Solid. static

Particle energy0

Solid: the least energy of the three states. The forces of attraction are very strong, so each particle can only vibrate on the spot. Drag right to give the particles energy.

Drag the slider to give the particles more energy, or take it away. 0 is the least energy and 5 the most: a scale for comparing, not a measurement.

Predict, then check

The slider made it look as if you need boiling to get a gas. Does that match what you see outside?

A puddle sits on the playground all day. It never gets anywhere near 100 °C, the temperature water boils at. By the evening it has gone. Could any of the water have turned into a gas, and if so, how?

Two ways a liquid becomes a gas

EvaporationvsBoiling

Tap each row to see why the difference matters.

Focus

What temperature?

Evaporation

Any temperature between the melting point and the boiling point

Boiling

One specific temperature for each substance: 100 °C for water

The insight

This is the big one. A liquid does not need to reach its boiling point to become a gas. Evaporation is already happening long before anything boils.

Where do particles become a gas?

Evaporation

Only at the surface: particles leave the liquid and mix with the air

Boiling

Within the liquid as well, not just at the surface

Any bubbles?

Evaporation

No bubbles form

Boiling

Bubbles of the substance in the gas state form within the liquid

Evaporation rate

?

Reason it through

Why does hotter water evaporate more quickly than cooler water?

Link 1 of 3

First link · your turn

You warm the water up. What happens to the energy of its particles?

2
Locked — reveal the link above first
3
Locked — reveal the link above first

Chemistry · Evaporation rate

Which one disappears first?

How fast each liquid evaporates

1 · Evaporates fastest3 · Evaporates slowest

  1. Ethanol

    The type of alcohol used in hand gel

  2. Water

  3. Acetone

    Nail varnish remover

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Why particles break free, why they settle back down, and how some escape early.

What you need to know

  • Say whether particles gain or lose energy when a substance melts, boils, condenses or freezes.
  • Describe what happens to the particles' movement and the forces of attraction in each change.
  • Explain how a puddle can evaporate without ever reaching its boiling point.
  • Tell evaporation and boiling apart, and explain why hotter liquids evaporate faster.

The big picture

Changes of state are all about energy. When particles gain enough energy they overcome the forces of attraction between them, so a solid melts and a liquid boils. When they lose energy they move less and come back together, so a gas condenses and a liquid freezes. Evaporation is the quiet one: particles at the surface of a liquid with enough energy escape as a gas, even well below the boiling point.

Key points

1Solid states have the least energy and gas states have the most. Particles gain or lose energy when a substance changes state.
2Particles that gain energy move more. In a solid they only vibrate on the spot, in a liquid they touch and move over and around each other, and in a gas they move freely in all directions.
3Melting and boiling: particles gain enough energy to overcome the forces of attraction, first enough to move past each other (melting), then enough to overcome them completely (boiling).
4Condensing and freezing: particles lose energy. A gas condenses as its particles move less and come together; a liquid freezes when its particles can only vibrate in fixed positions.
5Evaporation happens at the surface only, at any temperature between the melting point and the boiling point, with no bubbles. Boiling happens at one temperature (100 °C for water) with bubbles of gas within the liquid.
6In general, the higher the temperature, the faster the evaporation rate. Some substances evaporate faster than others: acetone, then ethanol, then water.

Worked example

Problem

A beaker of water sits on a bench at 40 °C. Over a day its level slowly drops. No bubbles are seen at any point. Is the water evaporating or boiling? Explain how you decide.

⚠ Watch out

Thinking a liquid has to reach its boiling point before any of it can become a gas. Boiling does need a specific temperature (100 °C for water), but evaporation happens at any temperature between the melting point and the boiling point, from the surface only.

🧠

Memory hook

Energy IN sets particles free: melt, then boil. Energy OUT lets them settle: condense, then freeze. Evaporation? That's the high-energy escapers slipping out through the surface.

✓

Check yourself

Cover the page. For melting, boiling, condensing and freezing, say whether the particles gain or lose energy. Then explain, in two sentences, how a puddle can dry up on a day nowhere near 100 °C.

Flashcards

(14)
Which state of matter has the least energy, and which has the most?
A solid has the least energy; a gas has the most.
How do the particles move in a solid, a liquid and a gas?
Solid: only vibrate on the spot. Liquid: touch and move over and around each other. Gas: move freely and randomly in all directions.
What happens to particles' movement when they gain energy?
They move more.
Melting (solid to liquid): what do the particles do?
Gain enough energy to overcome the forces holding them in fixed positions, so they can move past each other.
Boiling (liquid to gas): what do the particles do?
Gain enough energy to overcome the forces of attraction completely, so they can move freely in all directions.
Condensing (gas to liquid): what do the particles do?
Lose energy, move less and come together into the liquid state.
Freezing (liquid to solid): what do the particles do?
Lose energy, so they can no longer overcome the forces of attraction and can only vibrate in a fixed position.
What is evaporation?
When a particle at the surface of a liquid has enough energy to change to the gas state and mix with the air. It happens at the surface only.
Do all the particles in a liquid have the same energy?
No. Most stay in the liquid state, but some have enough energy to be in the gas state.
Can water evaporate below 100 °C?
Yes. Evaporation can happen at any temperature between the melting point and the boiling point.
Evaporation or boiling: which one makes bubbles?
Boiling: bubbles of gas form within the liquid. Evaporation makes no bubbles.
What is the evaporation rate?
A measure of how quickly a substance evaporates.
How does temperature affect the evaporation rate, and why?
In general, the higher the temperature, the faster the evaporation, because more particles have enough energy to be in the gas state.
Put water, ethanol and acetone in order of evaporation rate, fastest first.
Acetone (nail varnish remover), then ethanol (the alcohol in hand gel), then water.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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How this lesson was checked. This KS3 Chemistrylesson was published through Lightbulb Learning's human-designed editorial process — the educational standards, accuracy rules and publication checks it must pass were authored and approved by Philip Halpin. It passed subject-specific assessment, automated educational checks and technical publication verification before going live (publication checks completed 30 September 2026). Published pages are monitored, human spot-checking is ongoing across the lesson library, and anything found wrong is corrected or withdrawn. How our lessons are made and checked. Spotted a mistake? Email hello@lightbulblearning.co and we'll review it.