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.

a change of state of a substance from a solid directly to a gas; e.g. iodine.

when a substance changes from the gas state to the solid state without being in the liquid state.

State changes: evaporation and sublimation

Combined science

In the Separating Substances unit, pupils will build on their knowledge of states of matter to learn about different techniques for separating mixtures.

In the Solid, Liquid and Gas States and Changes of State unit, pupils learned about the properties of different states of matter and how particles move during changes of state.

This unit covers the particle model, states of matter, and changes between them, distinguishing physical from chemical changes. It explains the concept of purity in scientific terms, using melting point data to identify pure and impure substances, and explores the limitations of the particle model.

States of matter

Physical activity and equipment requiring safe use

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

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

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?

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?

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.

Match the numbers in the image below with the correct state change.

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

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

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

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

Match the following key terms with their definitions.

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 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.

Substances in the liquid state can evaporate at temperatures lower than their boiling point.

boiling off some of the water from the remaining tea

evaporation of some of the water from the remaining tea

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?

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

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

Which of these are examples of reversible changes of state?

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

Content guidance

Risk assessment required - equipment

Adult supervision required

Introduction

What will you need for this lesson?

Are you ready to learn?

Equipment

Content guidance

Supervision

Worksheet