Changes of state - Teacher Slides.pptx

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Changes of state

Particle model of matter

Lesson 2 of 6

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Warm-up

Particle model of matter

Lesson 2 of 6

Answer each one, then check.

1

What is the change from solid to liquid called?

2

What is the change from gas to liquid called?

3

What is the unit of mass?

4

What is freezing?

5

Give an example of a chemical change.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Warm-up - Answers

Particle model of matter

Lesson 2 of 6

1

What is the change from solid to liquid called?

Melting

2

What is the change from gas to liquid called?

Condensing

3

What is the unit of mass?

Kilogram

4

What is freezing?

Liquid to solid

5

Give an example of a chemical change.

Burning wood

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Learning Objectives

Particle model of matter

Lesson 2 of 6

1

Name each change of state.

2

Explain that mass is conserved in a change of state.

3

Explain that changes of state are physical changes and are reversible.

4

Draw and interpret particle diagrams for solids, liquids and gases.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Particle model of matter

Lesson 2 of 6

CHANGES OF STATE

Changes of state are physical changes: the material recovers its original properties if the change is reversed. Mass is conserved.

The particles are the same before and after, so the mass is the same. Only the arrangement and energy of the particles change.

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Six Changes of State

Particle model of matter

Lesson 2 of 6

Heating goes one way; cooling reverses it.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

The Changes

Particle model of matter

Lesson 2 of 6

Learn the names.

Change

From

To

Energy

Melting

Solid

Liquid

Energy taken in

Freezing

Liquid

Solid

Energy given out

Boiling or evaporating

Liquid

Gas

Energy taken in

Condensing

Gas

Liquid

Energy given out

Sublimation

Solid

Gas

Energy taken in

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Mass in a Change of State

Particle model of matter

Lesson 2 of 6

A 200 g ice cube melts to form water. What is the mass of the water? Explain.

1

Number of particles

The same particles are present as liquid water

2

Mass

Unchanged, because no particles are lost

ANSWER

200 g: mass is conserved.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Physical or Chemical?

Particle model of matter

Lesson 2 of 6

Explain why melting ice is a physical change but burning wood is a chemical change.

1

Melting ice

The water is the same substance, and it freezes back to ice with the same properties

2

Burning wood

New substances are made and the wood cannot be recovered

ANSWER

Physical changes are reversible and the material recovers its original properties.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Particle Explanation

Particle model of matter

Lesson 2 of 6

Say what the particles do.

Melting

Particles gain energy and break free from their fixed positions.

Boiling

Particles gain enough energy to overcome the attractions and move far apart.

Condensing and freezing

Particles lose energy and get closer.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Key Terms

Particle model of matter

Lesson 2 of 6

Melting

Solid to liquid.

Freezing

Liquid to solid.

Boiling

Liquid to gas throughout the liquid.

Evaporating

Liquid to gas at the surface.

Condensing

Gas to liquid.

Sublimation

Solid straight to gas.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Particle model of matter

Lesson 2 of 6

YOUR TASK

Name the Change

8 minutes

Name each change: (a) water becomes steam; (b) steam becomes water on a cold window; (c) a puddle freezes; (d) dry ice becomes carbon dioxide gas without becoming liquid.

1

Name the start and end state.

2

Choose the change.

WHAT A GOOD ANSWER SHOWS

(a) Boiling (or evaporating). (b) Condensing. (c) Freezing. (d) Sublimation.

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Can I...?

Particle model of matter

Lesson 2 of 6

Name all the changes of state.

Say whether energy is taken in or given out.

Explain that mass is conserved.

Explain physical changes.

Draw solid, liquid, gas particles.

Explain melting with particles.

Distinguish physical and chemical.

Give an example of sublimation.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Summary & Exam Focus

Melting, freezing, boiling, condensing, sublimation.

Mass is conserved.

Physical changes are reversible.

Particles' energy changes but the particles stay the same.

EXAM FOCUS

Name the change of state when a liquid becomes a solid. (1 mark)

Freezing.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Exam Practice: Changes of state

Particle model of matter

Lesson 2 of 6

Answer all questions. Use the mark allocation as a guide to how much to write. · 14 minutes

Question 1 · 3 marks · Complete

Name the change of state when (a) a solid changes to a liquid (b) a gas changes to a liquid (c) a solid changes to a gas without becoming a…

Question 2 · 2 marks · Explain

A 200 g ice cube melts. State the mass of the water and explain your answer.

Question 3 · 2 marks · Explain

Explain the difference between a physical change and a chemical change.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Exam Practice: Changes of state (cont.)

Particle model of matter

Lesson 2 of 6

Question 4 · 3 marks · Describe

Describe what happens to the arrangement and movement of the particles when a solid melts.

Question 5 · 3 marks · Explain

A student heats water until it boils. The water changes to steam. Explain, in terms of particles, why the steam takes up much more space…

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 1 · 3 marks · Complete

Particle model of matter

Lesson 2 of 6

“

Name the change of state when (a) a solid changes to a liquid (b) a gas changes to a liquid (c) a solid changes to a gas without becoming a liquid.

HOW TO ANSWER IT

Command word: Complete. Worth 3 marks, so plan before writing.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 1 · mark scheme

Particle model of matter

Lesson 2 of 6

3 marks available. Award a mark for each point made.

Melting

1 mark

Condensing

1 mark

Sublimation

1 mark

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 2 · 2 marks · Explain

Particle model of matter

Lesson 2 of 6

“

A 200 g ice cube melts. State the mass of the water and explain your answer.

HOW TO ANSWER IT

Command word: Explain. Worth 2 marks, so plan before writing.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 2 · mark scheme

Particle model of matter

Lesson 2 of 6

2 marks available. Award a mark for each point made.

200 g

1 mark

Mass conserved or the same number of particles

1 mark

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Question 3 · 2 marks · Explain

Particle model of matter

Lesson 2 of 6

“

Explain the difference between a physical change and a chemical change.

HOW TO ANSWER IT

Command word: Explain. Worth 2 marks, so plan before writing.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 3 · mark scheme

Particle model of matter

Lesson 2 of 6

2 marks available. Award a mark for each point made.

Physical: reversible with original properties

1 mark

Chemical: new substances

1 mark

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 4 · 3 marks · Describe

Particle model of matter

Lesson 2 of 6

“

Describe what happens to the arrangement and movement of the particles when a solid melts.

HOW TO ANSWER IT

Command word: Describe. Worth 3 marks, so plan before writing.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 4 · mark scheme

Particle model of matter

Lesson 2 of 6

3 marks available. Award a mark for each point made.

Solid: fixed regular positions, vibrating

1 mark

Gain energy

1 mark

Liquid: still close but move around each other

1 mark

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 5 · 3 marks · Explain

Particle model of matter

Lesson 2 of 6

“

A student heats water until it boils. The water changes to steam. Explain, in terms of particles, why the steam takes up much more space than the water.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 5 · mark scheme

Particle model of matter

Lesson 2 of 6

3 marks available. Award a mark for each point made.

Particles far apart in gas

1 mark

Close together in liquid

1 mark

Same mass, greater volume

1 mark

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