🔬 ScienceGrade 2Lesson 18
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Observe Heating and Cooling Effects
Lesson preview: the Mini Lesson and Vocabulary are open to everyone. Guided practice, exercises, the parent checklist and the printable PDF worksheet come with full access (free 7-day trial or membership).
Learning Objectives
- 1Name the four state-change processes: melting, freezing, evaporating, and condensing
- 2Match everyday substances to the state change that occurs when heated or cooled
- 3Explain that most heating and cooling state changes are reversible
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Mini Lesson
In Lesson 17 we learned that matter exists as a solid, liquid, or gas. Today we look closely at what causes matter to change from one state to another — and we observe those changes happening around us every day.
What heating does
- Melting — heat turns a solid into a liquid. The particles gain energy and break free from their fixed positions.
- Examples of melting: ice melts into water, a chocolate bar melts in your hand, a candle melts when its flame is lit.
- Evaporating — more heat turns a liquid into a gas. Particles gain so much energy they escape into the air.
- Examples of evaporating: a puddle dries up on a sunny day, water in a pot boils and becomes steam, wet clothes dry on a line.
What cooling does
- Freezing — cooling turns a liquid into a solid. Particles lose energy and lock together.
- Examples of freezing: water placed in a freezer becomes an ice cube, melted ice-cream mix is frozen to make solid ice cream.
- Condensing — cooling turns a gas into a liquid. Water vapor meets a cold surface and turns back into liquid droplets.
- Examples of condensing: water droplets form on the outside of a cold glass, a bathroom mirror fogs up after a hot shower.
Are these changes reversible?
- Yes, for most substances! You can melt ice and then refreeze it over and over.
- Some changes are not reversible — a cooked egg or burned toast cannot be uncooked.
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Ask yourself: "What are the four state-change words? Which two involve heating? Which two involve cooling?"
Vocabulary
Melting
A solid is heated until it becomes a liquide.g. ice to water, chocolate in your hand
Freezing
A liquid is cooled until it becomes a solide.g. water to ice cube in the freezer
Evaporating
A liquid is heated until it becomes a gase.g. a puddle drying in the sun
Condensing
A gas is cooled until it becomes a liquide.g. droplets forming on a cold glass
Reversible
A change that can go back and forth between statese.g. ice melts to water and freezes again
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