Internal energy - Teacher Slides.pptx

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Internal energy

Particle model of matter

Lesson 3 of 6

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Warm-up

Particle model of matter

Lesson 3 of 6

Answer each one, then check.

1

What is kinetic energy?

2

What is the equation for a change in thermal energy?

3

What is temperature a measure of?

4

What is a system?

5

What is potential energy?

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Warm-up - Answers

Particle model of matter

Lesson 3 of 6

1

What is kinetic energy?

Energy stored in moving objects

2

What is the equation for a change in thermal energy?

ΔE = mcΔθ

3

What is temperature a measure of?

How hot something is

4

What is a system?

An object or group of objects

5

What is potential energy?

Stored energy due to position or bonds

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Learning Objectives

Particle model of matter

Lesson 3 of 6

1

Define internal energy.

2

Explain how heating changes the energy stored within a system.

3

Use ΔE = mcΔθ to calculate the energy for a temperature change.

4

Distinguish temperature from internal energy.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Particle model of matter

Lesson 3 of 6

INTERNAL ENERGY

Internal energy is the total kinetic energy and potential energy of all the particles that make up a system.

Heating increases the energy of the particles. This either raises the temperature of the system or produces a change of state.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Where the Energy Goes

Particle model of matter

Lesson 3 of 6

Kinetic energy relates to temperature.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Temperature or Change of State?

Particle model of matter

Lesson 3 of 6

TEMPERATURE RISES

• The kinetic energy of the particles increases.

• The average speed of the particles increases.

• Calculate with ΔE = mcΔθ.

STATE CHANGES

• The potential energy of the particles increases.

• The particles move further apart or become free.

• The temperature stays the same.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Energy for a Temperature Rise

Particle model of matter

Lesson 3 of 6

Calculate the energy needed to raise the temperature of 0.50 kg of water from 20 °C to 60 °C. c = 4200 J/kg °C.

1

Temperature change

60 − 20 = 40 °C

2

Substitute

ΔE = 0.50 × 4200 × 40

3

Answer

ΔE = 84 000 J

ANSWER

84 000 J (84 kJ)

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Comparing Internal Energy

Particle model of matter

Lesson 3 of 6

Which has more internal energy: 1.0 kg of water at 50 °C or 2.0 kg of water at 50 °C?

1

Same temperature

The particles have the same average kinetic energy

2

Different mass

2.0 kg has twice as many particles, so twice as much total energy

ANSWER

2.0 kg of water has more internal energy.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Key Ideas

Particle model of matter

Lesson 3 of 6

Learn the links.

Temperature

Related to the average kinetic energy of the particles.

Internal energy

The total, including potential energy.

Heating

Increases internal energy by raising temperature or changing state.

Cooling

Decreases internal energy.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Key Terms

Particle model of matter

Lesson 3 of 6

Internal energy

The total kinetic and potential energy of all the particles in a system.

Kinetic energy

Energy of movement.

Potential energy

Energy stored because of forces between particles.

Specific heat capacity

Energy needed to raise 1 kg by 1 °C.

Temperature

A measure of the average kinetic energy of particles.

System

An object or group of objects.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Particle model of matter

Lesson 3 of 6

YOUR TASK

More Energy

10 minutes

Explain what happens to the internal energy and the temperature of a beaker of water as it is heated (a) from 20 °C to 60 °C (b) while ice at 0 °C is melting.

1

Say what changes in the particles.

2

Say what happens to temperature.

WHAT A GOOD ANSWER SHOWS

(a) Internal energy increases, mainly kinetic energy, so the temperature rises. (b) Internal energy increases as potential energy rises, but the temperature stays at 0 °C.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Can I...?

Particle model of matter

Lesson 3 of 6

Define internal energy.

Say heating increases internal energy.

Link kinetic energy to temperature.

Link potential energy to change of state.

Use ΔE = mcΔθ.

Compare two objects.

Explain cooling.

Use correct units.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Summary & Exam Focus

Internal energy = total kinetic + potential energy of the particles.

Heating raises temperature or changes state.

Temperature relates to kinetic energy.

ΔE = mcΔθ.

EXAM FOCUS

What is meant by the internal energy of a system? (2 marks)

The total kinetic and potential energy of all the particles.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Exam Practice: Internal energy

Particle model of matter

Lesson 3 of 6

Answer all questions. Use the mark allocation as a guide to how much to write. · 15 minutes

Question 1 · 2 marks · State

What is meant by the internal energy of a system?

Question 2 · 3 marks · Explain

A beaker of water is heated. Explain what happens to the energy stored within the water and to its temperature.

Question 3 · 3 marks · Calculate

Calculate the energy needed to raise the temperature of 0.50 kg of water from 20 °C to 60 °C. Specific heat capacity of water = 4200 J/kg…

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Exam Practice: Internal energy (cont.)

Particle model of matter

Lesson 3 of 6

Question 4 · 2 marks · Explain

1.0 kg of water and 2.0 kg of water are both at 50 °C. Which has more internal energy? Explain your answer.

Question 5 · 4 marks · Explain

Ice at 0 °C is heated and melts to water at 0 °C. Explain what happens to the internal energy and to the temperature during melting.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 1 · 2 marks · State

Particle model of matter

Lesson 3 of 6

“

What is meant by the internal energy of a system?

HOW TO ANSWER IT

Command word: State. Worth 2 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 3 of 6

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

Total of kinetic energy

1 mark

and potential energy of all the particles

1 mark

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 2 · 3 marks · Explain

Particle model of matter

Lesson 3 of 6

“

A beaker of water is heated. Explain what happens to the energy stored within the water and to its temperature.

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 2 · mark scheme

Particle model of matter

Lesson 3 of 6

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

Internal energy increases

1 mark

Particles gain kinetic energy

1 mark

Temperature rises

1 mark

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 3 · 3 marks · Calculate

Particle model of matter

Lesson 3 of 6

“

Calculate the energy needed to raise the temperature of 0.50 kg of water from 20 °C to 60 °C. Specific heat capacity of water = 4200 J/kg °C.

HOW TO ANSWER IT

Command word: Calculate. Worth 3 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 3 of 6

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

Temperature change 40 °C

1 mark

Correct substitution

1 mark

84 000 J

1 mark

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 4 · 2 marks · Explain

Particle model of matter

Lesson 3 of 6

“

1.0 kg of water and 2.0 kg of water are both at 50 °C. Which has more internal energy? 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 4 · mark scheme

Particle model of matter

Lesson 3 of 6

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

2.0 kg of water

1 mark

More particles so more total energy

1 mark

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 5 · 4 marks · Explain

Particle model of matter

Lesson 3 of 6

“

Ice at 0 °C is heated and melts to water at 0 °C. Explain what happens to the internal energy and to the temperature during melting.

HOW TO ANSWER IT

Command word: Explain. Worth 4 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 3 of 6

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

Internal energy increases

1 mark

Potential energy of particles increases

1 mark

Kinetic energy does not increase

1 mark

Temperature stays constant

1 mark

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