Learn · Science · Class 4

Melting, Freezing & Boiling

Changing state by heating and cooling, and why it is always reversible.

6 parts
Scroll to begin ↓
Turn this on and each part is read out as you reach it.
Heating and cooling change the stateSOLIDLIQUIDGASmeltboilfreezecondenseRed = heating · Blue = coolingWater melts at 0 °C and boils at 100 °C.
Red arrows are heating; blue arrows are cooling.
🧩 The partsMelting and freezingPart 2 of 6
✏️ Worked exampleBoiling and condensingPart 3 of 6
🔍 In detailA physical changePart 4 of 6
✅ SummaryState changer!Part 5 of 6
✏️ Worked exampleWatch one worked throughPart 6 of 6
1📘 DefinitionPart 1 / 6

Changing state

Heating and cooling can change a material from one state to another.

Solid → liquid → gas, and all the way back again.

Check yourself: Heating a solid until it turns to liquid is called…
2🧩 The partsPart 2 / 6

Melting and freezing

Melting: solid → liquid, by heating.

Freezing: liquid → solid, by cooling.

Water melts and freezes at 0 °C.

Check yourself: At what temperature does water freeze?
3✏️ Worked examplePart 3 / 6

Boiling and condensing

Boiling: liquid → gas, by heating. Water boils at 100 °C.

Condensing: gas → liquid, by cooling. That is why a cold glass gets wet on the outside.

Check yourself: At what temperature does water boil?
4🔍 In detailPart 4 / 6

A physical change

Changing state is a physical change, no new material is made.

Ice, water and steam are all still water. Freeze the water again and you get ice back.

Check yourself: Melted ice can be turned back into ice. This means the change is…
5✅ SummaryPart 5 / 6

State changer!

  • Melt (heat) ↔ freeze (cool) at 0 °C for water.
  • Boil (heat) ↔ condense (cool) at 100 °C.
  • Changing state is reversible: same material.
6✏️ Worked examplePart 6 / 6

Watch one worked through

Here is one done slowly, with the reason for every move. Then one for you.

Let me show you

Name the change of state and the temperature: ice becoming water, and water becoming steam.

  1. 🧊 → 💧 melting at 0 °C
    Solid to liquid is melting.
    Ice melts at 0 °C. That is the same temperature at which water freezes.
  2. 💧 → ☁️ boiling at 100 °C
    Liquid to gas is boiling.
    Water boils at 100 °C. Evaporation can happen below that, boiling cannot.
  3. melting + boiling = heat in freezing + condensing = heat out
    Heat goes IN for both of these.
    Going up a state takes heat in, coming down a state gives heat out.

Answer: Melting at 0 °C and boiling at 100 °C

Now you try

At what temperature does water freeze, in °C?

Show the answer

0

Practise Melting, Freezing & Boiling

Everything on QuizByt for Class 4 Science that goes with this lesson: read it first, then test yourself while it is fresh.

🧠 5 quizzes on Melting, Freezing & Boiling (2 easy, 2 medium, 1 hard)

Work up from easy to hard: the hard quiz asks the Class 4 exam-style questions on Melting, Freezing & Boiling.

🖨️ Printable worksheet

Melting, Freezing & Boiling on paper for Class 4, with room to write the working out. Preview the first page free.

🎮 Games for Class 4 Science

Memory and reasoning games at the right level for Class 4. Passing a quiz on Melting, Freezing & Boiling earns the credits that open them.

Next in Class 4 Science

All Science lessons · Every subject

Now test yourself

You have read the whole lesson. Take the quiz on this topic to see how much stuck,a free account is all it takes.

  • 📊 Your score is saved, so you can see progress over time
  • 🔍 See exactly which questions you got wrong, and why
  • 💎 Earn credits for every quiz you pass, and spend them on games
Create a free account →I already have one

In a hurry? Try a free Science quiz with no account.