# Changes of State

In this worksheet, students will study the arrangement of particles in the three states of matter (solids, liquids and gases) followed by the explanation of how they change from one to another.

Key stage:  KS 3

Curriculum topic:   Chemistry: The Particulate Nature of Matter

Curriculum subtopic:   Changes of State: Particle Model

Difficulty level:

### QUESTION 1 of 10

The three states of matter are solid, liquid and gas. In solids, particles are held in a fixed pattern by strong bonds, but they vibrate. In liquids, the bonds between particles are weaker than in solids and the particles are further from each other and free to move. In gases, particles are spread out widely and move faster than in solids and liquids.

The following diagram shows the arrangement of particles in the three states of matter and the terms used to describe the changes between the three states:

When a solid is heated and reaches its melting point, it melts into a liquid.

When a liquid reaches its boiling point, it evaporates into a gas.

When you cool down a gas, you can condense it back into liquid and a liquid turns into a solid, when it reaches its freezing point.

The freezing and melting point of a substance are always the same temperature.

Sublimation is when a solid turns straight into a gas.

Pure water becomes ice at 0 degrees Celsius and it boils at 100oC.

As the bonds that hold solid particles together are very strong, energy is needed to break them, so the particles start moving more freely when the substance becomes a liquid. When a solid turns back into a liquid, this energy is transferred to the surroundings, as it is no longer needed.

In order for our body to cool down, it produces sweat. Sweat uses heat from our body to evaporate.

Select TWO solid substances from the following options.

ice cream

ice

steam

oxygen

Match the state of matter with the correct particle arrangement. If you can't see the entire sentence in the box, hover your mouse over it.

## Column B

solid
particles are widely spread
liquid
particles are held fixed together by strong bonds
gas
particles are close together in a random pattern

What is the melting point of ice in degrees Celsius? Just type the number in the box below.

What is the freezing point of water in degrees Celsius? Just type the number in the box below.

What is the boiling point of water in degrees Celsius? Just type the number in the box below.

Complete the sentence by selecting one of the statements below:

Condensing is ..............

when a solids turns into a liquid.

when a solid turns into a gas.

when a liquid turns into a solid.

when steam becomes liquid water.

What is needed to break the bonds between solid particles so that it melts?

What is the scientific term for describing the change of a solid directly into a gas?

Tick the statement that describes what happens to particles in a liquid when they are heated to their boiling point.

Particles start moving more slowly and freeze.

Particles gain energy to move faster and further, so they escape from the liquid.

Particles lose energy and the liquid evaporates.

Particles move faster and condense into a liquid.

Sweat sublimates using heat from the body, true or false?

true

false

• Question 1

Select TWO solid substances from the following options.

ice cream
ice
EDDIE SAYS
Ice cream is solid when we take it out from the freezer and before it starts melting. Ice is the solid state of water.
• Question 2

Match the state of matter with the correct particle arrangement. If you can't see the entire sentence in the box, hover your mouse over it.

## Column B

solid
particles are held fixed together...
liquid
particles are close together in a...
gas
particles are widely spread
EDDIE SAYS
The three particle arrangements give the three states of matter their properties. See the diagram in the intro.
• Question 3

What is the melting point of ice in degrees Celsius? Just type the number in the box below.

0
EDDIE SAYS
As soon as ice is in 0°C it starts melting and the the temperature remains 0 until all of the ice melts.
• Question 4

What is the freezing point of water in degrees Celsius? Just type the number in the box below.

0
EDDIE SAYS
As soon as water reaches 0°C it starts freezing and the temperature remains at 0 until all of the water freezes. Did you notice that the melting point of ice and the freezing point of water is the same temperature? What is happening at that temperature?
• Question 5

What is the boiling point of water in degrees Celsius? Just type the number in the box below.

100
EDDIE SAYS
Water starts boiling at 100°C and the temperature remains at 100 until all of the water evaporates.
• Question 6

Complete the sentence by selecting one of the statements below:

Condensing is ..............

when steam becomes liquid water.
EDDIE SAYS
When a gas turns into a liquid we say it condenses. So, mercury vapour condenses into liquid mercury (357°C), oxygen condenses into liquid oxygen (-183°C), that sort of thing.
• Question 7

What is needed to break the bonds between solid particles so that it melts?

energy
EDDIE SAYS
Energy is needed for pretty much everything and the bonds between solids are so strong that needs energy to break them.
• Question 8

What is the scientific term for describing the change of a solid directly into a gas?

sublimation
sublime
sublimes
EDDIE SAYS
Some solids don't normally melt to form a liquid - they simply evaporate straight from the solid state. We say that these chemicals are subliming. Iodine crystals undergo sublimation: from iodine solid to iodine vapour. 'Dry ice' is the term used for solid CO2 . As this warms up, it doesn't melt - it sublimes directly into CO2 gas (which you cannot see - so what is the steamy stuff you see when dry ice is blown on to stage??).
• Question 9

Tick the statement that describes what happens to particles in a liquid when they are heated to their boiling point.

Particles gain energy to move faster and further, so they escape from the liquid.
EDDIE SAYS
This is how evaporation takes place; liquid particles gain enough energy to break free from the other particles. This is often because a fast-moving particle bangs into another one. This second one now gains sufficient energy to 'jump' out of the liquid state, from the surface of the liquid, and so become a gas particle (high energy state).
• Question 10

Sweat sublimates using heat from the body, true or false?

false
EDDIE SAYS
Sweat evaporates using heat from the body. It is a salty liquid, excreted from our pores. It uses body heat to gain sufficient energy to change from liquid to gas, thus taking the heat energy into the air with it and so ... cooling you down!
---- OR ----

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