Grade by Grade
E. Earth and Space Systems · Air and Water in the Environment

Ice, Water and Water Vapour

E2.4 E2.1 A1.2 A1.4About 40 minutes
Learning goals
  • I can name the three states of water: solid, liquid and gas.
  • I can find each state of water in the environment.
  • I can explain how warming and cooling change water from one state to another.
  • I can use the words melt, freeze, evaporate and condense.

Words to know

state
The form something is in: solid, liquid or gas.
solid
Matter that keeps its own shape. Ice is solid water.
water vapour
Water as a gas. It is invisible and mixed into the air.
melt
To change from a solid to a liquid when it warms up.
freeze
To change from a liquid to a solid when it cools down. Water freezes at 0°C.
evaporate
To change from a liquid to a gas (water vapour).
condense
To change from a gas back into tiny drops of liquid when it cools down.
temperature
How hot or cold something is, measured in degrees Celsius (°C).

Where did the puddle go?

After a spring rain, there is a big puddle on the sidewalk. The Sun comes out. By the afternoon, the puddle is gone!

Nobody mopped it up. Nobody drank it. So where did the water go?

Today you will find out. Water can change from one form to another.

A puddle on a sidewalk on a sunny spring day, with its edges already drying.
Look at the dry ring around this puddle. The Sun is warming the water, and it is slowly evaporating into the air. AI-generated image

Three states of water

Water can be in three states:

  1. Solid: ice. It keeps its own shape. Snow, icicles, frost, hail and glaciers are all solid water.
  2. Liquid: water. It flows. Rain, lakes, rivers, puddles and the water from your tap are liquid water.
  3. Gas: water vapour. It is invisible. It is mixed into the air all around us.

It is the same water in every state. Only its form changes.

🧊❄️💧🌊🌫️
Ice, snow, a raindrop, a lake and fog. Fog is a cloud near the ground made of tiny drops of liquid water floating in the air.

Warming and cooling change water's state

Temperature decides which state water is in.

  • Freezing: When liquid water cools down to 0°C, it freezes into ice.
  • Melting: When ice warms up above 0°C, it melts into liquid water.
  • Evaporating: When liquid water warms up, some of it evaporates and becomes water vapour, a gas that goes into the air. The warmer it is, the faster water evaporates. That is where the puddle went!
  • Condensing: When water vapour cools down, it condenses into tiny drops of liquid water. That is why a cold glass of milk gets wet on the outside on a hot day.

When water is heated to 100°C it boils. Big bubbles of water vapour form inside it.

ice(solid)water(liquid)water vapour(gas)meltwarm up:freeze(cool to 0°C)evaporatewarm up:condense(cool down)
Warming changes ice to water (melt) and water to water vapour (evaporate). Cooling changes water vapour to water (condense) and water to ice (freeze).

Remember from Grade 1

In Grade 1 you learned that water freezes at 0°C and that we measure temperature with a thermometer in degrees Celsius (°C). Now you will use that to explain how water changes.

Is steam water vapour?

The white cloud you see above a pot of boiling water is not water vapour. Water vapour is invisible! The white cloud is made of tiny drops of liquid water that formed when the vapour hit the cooler air and condensed.

Hot steam can burn you. Only watch boiling water from far away, with a grown-up.

Worked example

Let's explain it: The disappearing puddle

A puddle is on the driveway in the morning. The day is sunny and warm. By supper the puddle is gone. What happened?

  1. The Sun warmed the water in the puddle.
  2. Warm water evaporates faster. Bit by bit, the liquid water turned into water vapour.
  3. Water vapour is a gas. It is invisible, so we can't see it go up into the air.
  4. The water is not gone. It is now in the air as water vapour.

The puddle evaporated. The Sun's heat changed the liquid water into invisible water vapour in the air.

Worked example

Let's explain it: The "sweaty" glass

Leo takes a glass of ice water outside on a hot July day. Soon the outside of the glass is covered in drops. The glass is not leaking. Where did the drops come from?

  1. The air around us has invisible water vapour in it.
  2. The ice water makes the glass very cold.
  3. When the water vapour in the air touches the cold glass, it cools down.
  4. Cooled water vapour condenses into tiny drops of liquid water on the glass.

The drops came from water vapour in the air that condensed on the cold glass.

ChangeFromToWhat causes it?Example
meltsolid (ice)liquid (water)warming above 0°Csnowman melting in spring
freezeliquid (water)solid (ice)cooling to 0°Ca pond freezing in winter
evaporateliquid (water)gas (water vapour)warmingwet clothes drying on a line
condensegas (water vapour)liquid (water)coolingyour breath fogging a cold window
Four ways water changes state

A surprise about ice

Most things get smaller when they freeze. Water is different! When water freezes, it takes up a little more space.

That is why ice floats on top of a lake in winter. It is also why a full glass bottle of water left in the freezer can crack, and why water pipes can burst if they freeze in winter.

Just for fun

What did the ice cube say when it melted into a puddle?

"I've changed a lot... but I'm still the same water!"

Hands-on activity

Ice cube race and breath clouds

You need: 3 ice cubes the same size, 3 small plates, a clock, and a mirror or window.

  1. Predict: Where will an ice cube melt fastest: in the fridge, on the kitchen counter, or in a sunny window?
  2. Put one ice cube on a plate in each place at the same time. This is a fair test: same size cubes, same plates, same start time.
  3. Check every 10 minutes. Which one melts first? Why?
  4. Breath clouds: Put a small mirror in the fridge for 5 minutes. Take it out and breathe on it. What do you see? (Tiny drops! Water vapour in your breath condensed on the cold mirror.)
  5. Leave a wet cloth outside or on a drying rack. Check it later. Where did the water go?

Tell a grown-up which state of water you saw in each test and what change happened.

Safety: Stay away from boiling water and steam.

Your turn

1

Name the three states of water.

2

What happens to ice when it warms up above 0°C?

3

At what temperature does water freeze?

4

A wet towel dries on the clothesline. What change happened to the water?

5

Can you see water vapour?

6

You breathe on a cold window and it fogs up. What change happened?

7

Is snow a solid, a liquid or a gas?

More practice: warm-up

1

Is rain a solid, a liquid or a gas?

2

Is an icicle a solid, a liquid or a gas?

3

What do we call water as a gas?

4

What happens to a snowman on a warm spring day?

5

Which is warmer, 0°C or 20°C?

More practice: on your own

1

Why does a puddle dry up faster on a hot day than on a cool day?

2

Why does the outside of a cold juice box get wet on a hot day?

3

A pond is liquid in October and solid ice in January. What changed? Why?

4

Name the change for each: ice → water, water → ice.

5

Why does ice float on a lake?

Challenge

1

Maya says the white cloud over a boiling kettle is water vapour. Is she right? Explain.

2

In the ice cube race, the cube in the sunny window melted in 20 minutes and the one on the counter took 45 minutes. How much faster was the window cube? Why?

3

A grown-up leaves a full glass bottle of water in the freezer. It cracks. Explain why.

Check your understanding

Quiz

1.

Which is water in its gas state?

2.

A puddle dries up on a sunny day. The water...

3.

Water freezes at...

4.

Drops form on the outside of a cold glass because water vapour in the air...

5.

Which change needs warming?

6.

Why does ice float?

7.

Which is a solid form of water?

For parents and teachers

Big idea (E2.4): Water exists as a solid (ice), liquid (water) and gas (water vapour), and temperature changes move it between states: warming melts and evaporates; cooling condenses and freezes (at 0°C).

How to help: Point out state changes everywhere: frost on the car, a foggy bathroom mirror, laundry drying, ice melting in a drink. Ask "Which state? What change? Was it warming or cooling?"

Common misconceptions:

  • "Water vapour is the white steam." The visible cloud is condensed droplets. True water vapour is invisible.
  • "The puddle soaked into the ground." Some may, but on pavement most evaporates.
  • "The water on the cold glass leaked through." Show that drops form even on a sealed can, and that the drops are not coloured even if the drink is.
  • Boiling (100°C) is not the only way water becomes vapour; evaporation happens at any temperature, faster when warm.

Safety (A1.4): Keep children away from boiling water and steam. The ice cube race is a simple fair test (A1.2): keep everything the same except the location.