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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 7.4

Year 4 Science: Condensation

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

7.4

Condensation

Year 4
M3: identify the part played by condensation in the water cycle
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.

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