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Primary Science · Year 4Chapter 7 · Changing state and the water cycle
Year 4 Science · Changing state and the water cycle · Lesson 7.1

Year 4 Science: Changing state: melting and freezing

Part of the Year 4 Science changing state and the water cycle chapter. Chapter overview · whole chapter on one page

7.1

Changing state: melting and freezing

Year 4
M2: observe that some materials change state when they are heated or cooled
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.

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