Websink Prep UKKS2 ScienceYear 4 chaptersScience textbooksYear 1Year 2Year 3Year 4Year 5Year 6Year 7Year 8Year 9Browse allPast papersFind a tutorBecome a tutor
Primary Science · Year 4Chapter 7 · Changing state and the water cycle
Year 4 · Chapter 7

Changing state and the water cycle

By the end of this chapter you will be able to

  • Name the changes of state: melting, freezing, evaporation and condensation
  • Say that some materials change state when they are heated or cooled
  • Read the temperature at which water freezes and boils, in degrees Celsius
  • Compare how quickly something dries or melts in places with different temperatures
  • Explain condensation and evaporation, and say which part each plays in the water cycle
  • Put the four stages of the water cycle in order, and explain how they connect

You should already know

  • Solids, liquids and gases, and how each behaves (Year 4 Science, Chapter 6)
  • Measuring with a thermometer in degrees Celsius (Year 4 Science, Chapter 1)

Where this leads

  • Changes of state in more detail, including the particle model (Year 6 Science)
  • Weather and the water cycle in the wider environment (Year 4 Science, Chapter 4 and Year 5 Science)

National Curriculum for England, Key Stage 2 science, Year 4. Content: M2 observe that some materials change state when they are heated or cooled, and measure or research the temperature at which this happens in degrees Celsius (°C), M3 identify the part played by evaporation and condensation in the water cycle, and associate the rate of evaporation with temperature.

Exercise P  Do you remember?

1
FWhich tool measures temperature? Write the word: thermometer or ruler.
2
FIs ice a solid or a liquid? Write the word.
3
FName one liquid. Write one liquid.
4
FDo clouds form in the sky from water? Write yes or no.
5
FWhat is the name of the gas in the bubbles in fizzy water? Write the name.
7.1

Changing state: melting and freezing

Year 4
M2: observe that some materials change state when they are heated or cooled
Video lesson: Changing state: melting and freezingComing soon
Story. Yusuf leaves an ice cube on the windowsill, and then another in the shady corner of the kitchen. “Which one will melt first?” he asks. Ms Chen says, “Let us find out, and time them both.”

Some materials can change state. This means they change from a solid to a liquid, or from a liquid to a solid. Changes of state happen when a material is heated or cooled.

When a solid is heated and turns into a liquid, it is melting. When a liquid is cooled and turns into a solid, it is freezing. Ice melts when it is heated, and water freezes when it is cooled.

SolidLiquidGasmeltingfreezingevaporationcondensationheating moves the arrows to the right; cooling moves them to the left(orange = heated, blue = cooled)
Three states of matter. Heating makes a solid melt and a liquid evaporate. Cooling makes a liquid freeze and a gas condense.

Yusuf timed two ice cubes, both the same size. The table shows how long each one took to melt.

PlaceMinutes to melt
Warm room, 22 degrees Celsius20
Cool room, 12 degrees Celsius40

Key ideas

  • Melting is when a solid changes into a liquid, by heating.
  • Freezing is when a liquid changes into a solid, by cooling.
  • Some materials change state when they are heated or cooled.
  • The warmer the place, the faster ice melts.
Worked example 7.1.1
Ice is heated and turns into water. Is this melting or freezing? Write the word.

Method. Think about the change.

  1. Read the change. The ice is a solid that becomes a liquid when heated.
    solid to liquid
  2. Name the change. A solid that turns into a liquid by heating is melting.
    melting
  3. Write the answer.
    melting

Check. Melting is caused by heating. ✓

Worked example 7.1.2
Water in a freezer turns into ice. Is this melting or freezing? Write the word.

Method. Think about the change.

  1. Read the change. The water is a liquid that becomes a solid when it is cooled.
    liquid to solid
  2. Name the change. A liquid that turns into a solid by cooling is freezing.
    freezing
  3. Write the answer.
    freezing

Check. Freezing is caused by cooling. ✓

Worked example 7.1.3
Which place melted the ice faster: the warm room or the cool room? Write the name of the place.

Method. Compare the two times in the table.

  1. Read the times. The warm room took 20 minutes. The cool room took 40 minutes.
    20 and 40
  2. Choose the faster. The shorter time is for the warm room, so it melted faster.
    warm room
  3. Write the answer.
    Warm room

Check. Warmer places melt ice faster. ✓

Watch out

Watch out: a material does not change state just because it is cold. It changes state when its temperature is high enough, or low enough, for that material.

Try it at home or school (with a grown-up). With a grown-up, place two ice cubes in two dishes, one in a sunny spot and one in a shady spot indoors. Look at them every 10 minutes, and write down what you see. Do not put ice in your mouth, and dry the floor if it gets wet.

Exam tip

Grown-up tip. Ask: “Which one is melting faster? Why do you think that is?” Let your child time each cube and write the results in a table.

Exercise 7A  Changing state: melting and freezing

1
FWhat is the word for a solid that turns into a liquid when it is heated? Write the word.
2
FWhat is the word for a liquid that turns into a solid when it is cooled? Write the word.
3
FIce is heated and becomes water. Is this melting or freezing? Write the word.
4
FWater in a freezer becomes ice. Is this melting or freezing? Write the word.
5
FDoes heating some materials make them change state? Write yes or no.
6
FFill in the gap: a material that melts when it is heated can be made solid again by ___. Write the word.
7
FCandle wax melts when it is heated. Is the wax changing state? Write yes or no.
8
FLook at the table in section 7.1. How many minutes did the ice take to melt in the cool room? Write the number.
9
PSLook at the table in section 7.1. How many minutes longer did the cool room take than the warm room? Write the number.
10
PSIs it correct to say that ice can only melt inside a freezer? Write yes or no.
11
PSWorking scientifically. Predict which ice cube will melt faster: one in the sun, or one in the shade. Write one prediction with a reason.
12
RExplain why ice melts faster in a warm room than in a cool room. Write one sentence.
7.2

The temperature at which water changes state

Year 4
M2: measure or research the temperature at which this happens in degrees Celsius (°C)
Video lesson: The temperature at which water changes stateComing soon
Story. Mr Patel asks the class, “At what temperature does water freeze?” Priya says, “I can read it on the thermometer, when the water turns to ice.” Mr Patel says, “Good. The temperature at which a change of state happens is always the same for the same material.”

Each material changes state at a particular temperature, which we measure in degrees Celsius (°C). For water, the important temperatures are:

WaterTemperature (degrees Celsius)What happens
Ice0melts to water, or water freezes to ice
Water100boils, and turns into water vapour
0255075100ice melts, water freezes: 0 degreeswater boils: 100 degreesdegrees Celsius
A temperature scale from 0 to 100 degrees Celsius. Ice melts and water freezes at 0; water boils at 100.

Key ideas

  • Water freezes at 0 degrees Celsius, and ice melts at 0 degrees Celsius.
  • Water boils at 100 degrees Celsius.
  • Temperatures are measured in degrees Celsius, with a thermometer.
  • The temperature for a change of state is the same each time for the same material.
Worked example 7.2.1
At what temperature in degrees Celsius does water freeze? Write the number.

Method. Read the table.

  1. Read the table. Water freezes at the same temperature that ice melts.
    the same
  2. Read the number. That temperature is 0 degrees Celsius.
    0
  3. Write the answer.
    0

Check. Ice melts at 0 degrees Celsius too. ✓

Worked example 7.2.2
How many degrees Celsius is it from freezing to boiling for water? Write the number.

Method. Subtract the freezing temperature from the boiling temperature.

  1. Read the two numbers. Water freezes at 0 and boils at 100 degrees Celsius.
    0 and 100
  2. Subtract. 100 minus 0 is 100.
    100 - 0 = 100
  3. Write the answer.
    100

Check. The range from freezing to boiling is 100 degrees. ✓

Worked example 7.2.3
Water boils at what temperature in degrees Celsius? Write the number.

Method. Read the table.

  1. Read the boiling row. The boiling row says 100 degrees Celsius.
    100
  2. Check the picture. The right-hand end of the scale in the picture is also 100.
    right-hand end
  3. Write the answer.
    100

Check. The scale in the picture ends at 100. ✓

Watch out

Watch out: a temperature of 0 degrees Celsius is not the same as no temperature. It is the temperature at which water freezes.

Try it at home or school (with a grown-up). Look at a kitchen thermometer, or a thermometer in a window, with a grown-up. Read the temperature in degrees Celsius. Do not touch any hot water, and never boil water yourself.

Exam tip

Grown-up tip. Ask: “What does the thermometer say? Is it above or below 0 degrees?” Let your child find 0 and 100 on a thermometer picture, and point to each one.

Exercise 7B  The temperature at which water changes state

1
FWhat temperature does water freeze at, in degrees Celsius? Write the number.
2
FWhat temperature does ice melt at, in degrees Celsius? Write the number.
3
FWhat temperature does water boil at, in degrees Celsius? Write the number.
4
FHow many degrees Celsius is it from freezing to boiling for water? Write the number.
5
FLook at the scale in section 7.2. What is the number at the right-hand end? Write the number.
6
FIs 0 degrees Celsius the temperature at which water freezes? Write yes or no.
7
FWhich tool do we use to measure temperature in degrees Celsius? Write the word.
8
FWhich is hotter: 20 degrees Celsius or 0 degrees Celsius? Write the number.
9
PSA child says water boils at 50 degrees Celsius. Is the child right? Write yes or no.
10
PSRuby says the freezing temperature of water is 10 degrees Celsius. Is Ruby right? Write yes or no.
11
PSWorking scientifically. Plan how you would find the temperature at which ice starts to melt, using a thermometer. Write one thing you would keep the same.
12
RExplain why the thermometer bulb must be in the water, and not touching the bottom of the cup, when you measure the temperature. Write one sentence.
7.3

Evaporation

Year 4
M3: identify the part played by evaporation in the water cycle, and associate the rate of evaporation with temperature
Video lesson: EvaporationComing soon
Story. Aisha wets three cloths and hangs one on the sunny windowsill, one in the shady corner and one in the cool hallway. “Which one will dry first?” she asks. “Let us time them,” says Mr Patel.

Evaporation is when a liquid changes into a gas. Water at the surface of a puddle, a lake, the sea or a wet cloth turns into water vapour, which is a gas, and goes into the air. Evaporation happens at any temperature, but it happens faster when it is warmer.

The table shows the results of the drying test. The fastest result has the smallest number of minutes.

PlaceTemperature (degrees Celsius)Minutes to dry
Sunny windowsill2830
Shady corner1860
Cool hallway1290
0306090minutes to dry30 minSunny windowsill28 degrees60 minShady corner18 degrees90 minCool hallway12 degrees
The minutes to dry in each place: 30 minutes in the sunny windowsill, 60 in the shady corner, and 90 in the cool hallway.

Key ideas

  • Evaporation is when a liquid changes into a gas.
  • Evaporation happens faster when it is warmer.
  • Evaporation is part of the water cycle.
  • A wet cloth dries faster in a warm place than in a cool place.
Worked example 7.3.1
Which place dried the cloth fastest? Write the name of the place.

Method. Find the smallest number of minutes.

  1. Read the minutes. The minutes are 30, 60 and 90.
    30 is the smallest
  2. Name the place. The sunny windowsill took 30 minutes, the fastest.
    Sunny windowsill
  3. Write the answer.
    Sunny windowsill

Check. The sunny windowsill was the warmest place. ✓

Worked example 7.3.2
How many minutes faster was the sunny windowsill than the shady corner? Write the number.

Method. Subtract the two times.

  1. Read the two times. The shady corner took 60 minutes, and the sunny windowsill took 30.
    60 and 30
  2. Subtract. 60 minus 30 is 30.
    60 - 30 = 30
  3. Write the answer.
    30

Check. Check: 30 plus 30 makes 60. ✓

Worked example 7.3.3
Is evaporation faster when the place is warmer? Write yes or no.

Method. Look at the temperatures and the times together.

  1. Compare them. The warmest place, 28 degrees, dried fastest, in 30 minutes.
    warmest, fastest
  2. Decide. So evaporation is faster when it is warmer, and the answer is yes.
    yes
  3. Write the answer.
    yes

Check. The pattern is the same for all three places. ✓

Watch out

Watch out: evaporation is not the same as boiling. Evaporation happens at the surface of the liquid at any temperature, while boiling needs a high temperature.

Try it at home or school (with a grown-up). Wet two tea towels with a grown-up. Hang one on a sunny windowsill and one in a shady place, and check each one every 30 minutes. Write down which dries first. Do not use hot water.

Exam tip

Grown-up tip. Ask: “Which towel dried first? Was it the warm place or the cool place?” Let your child time the towels and write the results in a table.

Exercise 7C  Evaporation

1
FWhat is the word for when a liquid changes into a gas at its surface? Write the word.
2
FWhich place dried the cloth fastest? Write the name of the place.
3
FWhich place dried the cloth slowest? Write the name of the place.
4
FHow many minutes did the cloth take to dry in the shady corner? Write the number.
5
FThe sunny windowsill was 28 degrees Celsius. What was the temperature of the cool hallway? Write the number.
6
FIs evaporation faster when it is warmer? Write yes or no.
7
FDoes evaporation happen in the cool hallway? Write yes or no.
8
PSHow many minutes faster was the sunny windowsill than the cool hallway? Write the number.
9
PSWhich dries faster: a warm towel or a cold towel? Write the word: warm or cold.
10
PSRuby says the cloth dried faster in the cool hallway because it was cooler. Is Ruby right? Write yes or no.
11
PSWorking scientifically. Predict which will dry faster: a puddle in the sun, or a puddle in a shady place. Write one prediction with a reason.
12
RExplain why washing hung outside on a warm, windy day dries quickly. Write one sentence.
7.4

Condensation

Year 4
M3: identify the part played by condensation in the water cycle
Video lesson: CondensationComing soon
Story. Leo takes a cold drink from the fridge and puts it on the table. Soon, drops of water form on the outside of the glass. “Where has the water come from?” he asks. Mr Patel says, “From the air. Water vapour in the warm air cools on the glass, and it turns back into drops.”

Condensation is when a gas changes back into a liquid. Water vapour in the air cools, and turns into tiny drops of water. This is the opposite of evaporation.

We see condensation on a cold glass, on a cold mirror when you breathe on it, and as dew on grass on a cool morning. In the sky, condensation forms the clouds.

Key ideas

  • Condensation is when water vapour cools and changes into a liquid.
  • Condensation is the opposite of evaporation.
  • Drops on the outside of a cold drink are caused by condensation.
  • Clouds form in the sky when water vapour cools and condenses.
Worked example 7.4.1
Water vapour in the warm air cools on a cold glass, and drops form. What is this change called? Write the word.

Method. Read the description.

  1. Read the change. A gas (water vapour) cools and turns into a liquid (drops).
    gas to liquid
  2. Name the change. A change from gas to liquid by cooling is condensation.
    condensation
  3. Write the answer.
    condensation

Check. Condensation makes drops on a cold surface. ✓

Worked example 7.4.2
Where do the drops form on a cold drink in a warm room: inside or outside the glass? Write the word.

Method. Think about where the warm air is.

  1. Think about the air. The warm air is outside the glass, and it touches the cold surface.
    outside
  2. Decide. So the drops form on the outside of the glass.
    outside
  3. Write the answer.
    outside

Check. The drops come from the warm air around the glass. ✓

Worked example 7.4.3
Is condensation a change from a gas to a liquid? Write yes or no.

Method. Think about the change.

  1. Think about the states. Condensation changes water vapour, which is a gas, into a liquid.
    gas to a liquid
  2. Decide. So the answer is yes.
    yes
  3. Write the answer.
    yes

Check. Evaporation is the other way round. ✓

Watch out

Watch out: condensation does not take water away from the air. It changes water vapour in the air back into liquid drops.

Try it at home or school (with a grown-up). Breathe onto a clean, cold window or a cold mirror with a grown-up. Watch the mist form, and then fade. Say what has happened to the water vapour from your breath. Do not breathe onto anything that is not clean.

Exam tip

Grown-up tip. Ask: “Where did the mist come from? What happened to it when it went?” Let your child explain condensation and evaporation in their own words.

Exercise 7D  Condensation

1
FWhat is the word for a gas that changes back into drops of liquid when it cools? Write the word.
2
FWhere do the drops form on a cold glass of drink: outside or inside? Write the word.
3
FDoes condensation happen on a cold glass? Write yes or no.
4
FWhat forms in the sky when water vapour cools high up? Write the word.
5
FIs condensation a change from a gas to a liquid? Write yes or no.
6
FIs evaporation a change from a liquid to a gas? Write yes or no.
7
FWhat is the word for the mist that forms on a cold mirror when you breathe on it? Write the word.
8
FWhich change is the opposite of evaporation: condensation or melting? Write the word.
9
FDew forms on grass on a cool morning. Is the dew formed by condensation or evaporation? Write the word.
10
PSAli says condensation takes water away from the air. Is Ali right? Write yes or no.
11
PSWorking scientifically. Plan a safe test to show condensation on a cold drink. Write one thing you must keep the same each time.
12
RExplain where the water on the outside of a cold drink comes from. Write one sentence.
7.5

The water cycle

Year 4
M3: identify the part played by evaporation and condensation in the water cycle
Video lesson: The water cycleComing soon
Story. Ruby asks, “If the sea gets smaller when the sun shines, where does the water go?” Mr Patel says, “Up into the air. Then it comes back down as rain, and flows into rivers and the sea again. We call this the water cycle.”

The water cycle is the way water moves around the Earth. The picture shows the four main stages, and the table describes each one.

cloudseariver1 evaporation2 condensation3 rain4 collection
The water cycle: 1 evaporation from the sea, 2 condensation into a cloud, 3 rain falls, 4 water collects in rivers and the sea.

The four stages happen in order. The cycle has no start or end, because the water goes round and round.

StageWhat happens
Evaporationthe sun heats water in seas, lakes and puddles, and it turns into water vapour, a gas
Condensationwater vapour cools high in the air, and turns back into tiny droplets, which make clouds
Precipitationthe droplets join together and fall as rain, snow or hail
Collectionthe water collects in rivers, lakes and the sea, and the cycle starts again

Key ideas

  • Evaporation: the sun heats water, and it turns into water vapour.
  • Condensation: water vapour cools, and forms tiny drops that make clouds.
  • Precipitation: the drops join together and fall as rain, snow or hail.
  • Collection: the water gathers in rivers, lakes and the sea.
Worked example 7.5.1
In the water cycle, which stage is when the sun heats water and it turns into water vapour? Write the word.

Method. Read the table of stages.

  1. Read the first stage. The first stage is when the sun heats water into water vapour.
    heats water
  2. Name the stage. This stage is evaporation.
    evaporation
  3. Write the answer.
    evaporation

Check. Evaporation is the first stage in the cycle. ✓

Worked example 7.5.2
Which stage forms clouds in the sky? Write the word.

Method. Read the table of stages.

  1. Read the second stage. Water vapour cools and forms tiny drops that make clouds.
    make clouds
  2. Name the stage. This stage is condensation.
    condensation
  3. Write the answer.
    condensation

Check. Clouds form by condensation. ✓

Worked example 7.5.3
What is the stage after condensation in the water cycle? Write the word.

Method. Read the order of the stages.

  1. Find condensation. Condensation is the second stage.
    second
  2. Name the next stage. The third stage is precipitation, when the drops fall as rain.
    precipitation
  3. Write the answer.
    precipitation

Check. Rain falls after the clouds have formed. ✓

Watch out

Watch out: the water cycle does not use up water. The same water goes round and round, from the sea to the air and back again.

Try it at home or school (with a grown-up). Put a little water in a clear jar with a grown-up, and cover it with cling film held in place with an elastic band. Put it in a sunny place. Look for drops forming under the film after a few hours. Do not use hot water.

Exam tip

Grown-up tip. Ask: “Where did the water go? Where did the drops come from? Where will the water go next?” Let your child name each stage of the water cycle, in order.

Exercise 7E  The water cycle

1
FWhich stage of the water cycle is when the sun heats water and it becomes water vapour? Write the word.
2
FWhich stage makes clouds? Write the word.
3
FWhich stage is rain, snow or hail falling to the ground? Write the word.
4
FWhich is the last stage in the water cycle? Write the word.
5
FHow many stages are in the water cycle in section 7.5? Write the number.
6
FWhich stage of the water cycle comes first: evaporation or collection? Write the word.
7
FWater vapour is a gas. Which state of matter is it? Write the word: solid, liquid or gas.
8
FWhich stage fills the rivers, lakes and the sea? Write the word.
9
PSRain comes from clouds. Which stage came just before the rain, and made the clouds? Write the word.
10
PSRuby says water in the sea is lost forever once it has evaporated. Is Ruby right? Write yes or no.
11
PSWorking scientifically. Predict what will happen to a puddle on a hot, sunny day. Write one prediction with a reason.
12
RExplain how the sun helps the water cycle. Write one sentence.

Chapter summary

SkillMethod
Changing stateMelting: solid to liquid, by heating. Freezing: liquid to solid, by cooling.
Temperatures of waterWater freezes and ice melts at 0 degrees Celsius. Water boils at 100 degrees Celsius.
EvaporationA liquid turns into a gas at its surface. It is faster when the place is warmer.
CondensationA gas cools and turns into drops of liquid. It forms clouds, dew and drops on a cold glass.
The water cycleEvaporation, condensation, precipitation and collection. The water goes round and round.

Can you…?

  • I can name melting, freezing, evaporation and condensation
  • I can say that some materials change state when they are heated or cooled
  • I can read the temperatures at which water freezes and boils, in degrees Celsius
  • I can say that evaporation is faster when it is warmer
  • I can explain condensation and evaporation, and their parts in the water cycle
  • I can put the four stages of the water cycle in order

Key terms

change of state
when a material changes from a solid, to a liquid, or to a gas, or back again
melting
when a solid changes into a liquid, by heating
freezing
when a liquid changes into a solid, by cooling
evaporation
when a liquid changes into a gas at its surface
condensation
when a gas cools and changes into a liquid
water vapour
water in the form of a gas, in the air
precipitation
water that falls from clouds as rain, snow or hail
water cycle
the way water moves round the Earth, through evaporation, condensation, precipitation and collection
degrees Celsius
the unit used to measure temperature, written °C

Exercise 7Z  Check-up

1
What is the word for a solid that turns into a liquid when it is heated? Write the word.
2
At what temperature in degrees Celsius does water freeze? Write the number.
3
At what temperature in degrees Celsius does water boil? Write the number.
4
Which of the two places dried a cloth fastest in section 7.3: the sunny windowsill or the cool hallway? Write the name.
5
Ice melted in 20 minutes in a warm room, and in 40 minutes in a cool room. How many minutes longer did the cool room take? Write the number.
6
What is the word for a gas that changes back into drops of liquid when it cools? Write the word.
7
Which stage of the water cycle forms clouds? Write the word.
8
Name the stage of the water cycle when the drops fall as rain, snow or hail. Write the word.
9
Ali says a puddle dries up faster in a cool place than a warm place. Is Ali right? Write no, and give one reason.
10
Explain how condensation and evaporation are linked in the water cycle. Write one sentence.

Total 16 marks. Allow about 16 minutes.

Exercise 7X  Practice test questions

1
FWhen a solid is heated and turns into a liquid, what is the name of this change? Write the word.[1 mark]
2
FAt what temperature in degrees Celsius does water boil? Write the number.[1 mark]
3
FAt what temperature in degrees Celsius does water freeze? Write the number.[1 mark]
4
FWater vapour in the air cools and turns into tiny drops. Write the word for this change.[1 mark]
5
FA wet cloth dried in 30 minutes on a sunny windowsill, and in 90 minutes in a cool hallway. Which place was faster? Write the name of the place.[2 marks]
6
PSIce melted in 20 minutes in a room at 22 degrees Celsius, and in 40 minutes in a room at 12 degrees Celsius. How many minutes longer did the cooler room take? Write the number.[2 marks]
7
FWrite the four stages of the water cycle in the order they happen, starting with evaporation.[2 marks]
8
FWrite the word for the change where a liquid turns into a gas at its surface, such as a puddle drying up.[1 mark]
9
RExplain why a puddle dries up faster on a hot day than on a cool day. Write one sentence.[3 marks]
10
FWater in the sea turns into water vapour, which later forms clouds. Write the name of the stage that changes water vapour into clouds.[2 marks]
← Chapter 6: Solids, liquids and gasesChapter 8: Sound →

Websink Prep UK is an independent site. It is not affiliated with, endorsed by or sponsored by AQA, Pearson Edexcel, OCR, WJEC, Eduqas, CCEA, SQA, GL Assessment, CEM or the Department for Education. All exam board names and trademarks belong to their owners. Past papers are linked from the exam boards' own websites and are not hosted here.

About Websink Prep UK · Find a tutor · Privacy · Terms · Cookie settings