State changes: evaporation and sublimation | Combined science

Starter quiz

Some students are revising the differences between boiling and evaporating, and they mix up their revision cards. Select all the statements below that are about evaporation.

A liquid is heated and the volume reduces, but no bubbles of gas form. ✓

A process that can take place at any temperature above melting point. ✓

Cooking pasta in a pot of water that is producing a lot of bubbles of gas.

Forming a gas from a liquid, but a specific temperature needs to be reached.

Some spilled water dries in a cold room. ✓
Substances in the liquid state can evaporate at temperatures lower than their boiling point.

True ✓

False
A cup with some hot tea is left in a cold room. The image shows you what it looks like after a day or so. What has happened?

boiling off some of the water from the remaining tea

condensation of water from the air

evaporation of some of the water from the remaining tea ✓

evaporation of some of the remaining tea
Solid and liquid states of water are obvious in this image. What clearly indicates that there is also water present in the gas state?

the colour of the water around the iceberg

the presence of clouds - they form when water vapour condenses ✓

the presence of ice - it forms when water freezes
Which of these are examples of reversible changes of state?

condensation ✓

evaporation ✓

freezing ✓

heating

melting ✓
When using the particle model, which image best represents an individual particle from a substance in the gas state?

particle 1

particle 2

particle 3 ✓

Exit quiz

What are three crucial assumptions we have to make about the states of matter and the particle model?

all changes of states happen all the time at all temperatures

all matter consists of particles, the smallest unit of matter ✓

all matter exists in all states in nature

all particles are attracted to each other, to a larger or smaller extent ✓

all particles move; even in solids the particles vibrate at their fixed position ✓
Which of the three crucial assumptions means that we can explain how it is possible that particles can go directly from the solid state to the gas state?

all matter consists of particles, the smallest unit of matter

all particles are attracted to each other, to a larger or smaller extent

all particles move; even in solids the particles vibrate at their fixed position ✓
Which of the three crucial assumptions means that we can explain how it is possible that particles can go directly from the gas state to the solid state?

all matter consists of particles, the smallest unit of matter

all particles are attracted to each other, to a larger or smaller extent ✓

all particles move; even in solids the particles vibrate at their fixed position
For evaporation to take place, particles have to have enough energy, even if the liquid is not at boiling point. The other requirement is that such a particle is at the ______ of the liquid.

'surface' ✓
Match the numbers in the image below with the correct state change.

1

⇔

sublimation ✓

2

⇔

condensation ✓

3

⇔

deposition ✓

4

⇔

boiling and/or evaporation ✓

5

⇔

melting ✓

6

⇔

freezing ✓
Match the following key terms with their definitions.

condensation

⇔

when a substance in gas state is cooled and changes to liquid state ✓

deposition

⇔

a change of state of a substance from a gas directly to a solid ✓

evaporation

⇔

if surface particle in liquid has enough energy to change to gas state ✓

sublimation

⇔

a change of state of a substance from a solid directly to a gas ✓

Worksheet

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Lesson Details

Key learning points

Sublimation is the change from solid to gas; deposition is the change from gas to solid, both bypass the liquid state.
Sublimation and deposition occur at specific conditions of temperature and pressure.
Energy changes in sublimation/deposition are similar to melting/freezing but happen directly between solid and gas.
Evaporation is when a liquid changes to gas at the surface as particles gain enough energy to overcome forces.

Common misconception

Pupils think that substances need to be at their boiling point temperature to evaporate.

Use plenty of real life examples of liquids evaporating in situations where pupils know that the liquid is not above its boiling point but still evaporates.

Keywords

Evaporation - when a particle of a substance in the liquid state at the surface, has enough energy to change to the gas state and mix with air.
Sublimation - a change of state of a substance from a solid directly to a gas; e.g. iodine.
Deposition - when a substance changes from the gas state to the solid state without being in the liquid state.