AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Internal energy
Particle model of matter · Lesson 3 of 6
Warm-up
Answer each one, then check.
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
Learning Objectives
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.
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.
Where the Energy Goes
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Kinetic energy relates to temperature. |
Heating raises either the kinetic energy of particles, raising temperature, or their potential energy, changing state.
Temperature or Change of State?
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TEMPERATURE RISES |
STATE CHANGES |
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▸ The kinetic energy of the particles increases. ▸ The average speed of the particles increases. ▸ Calculate with ΔE = mcΔθ. |
▸ The potential energy of the particles increases. ▸ The particles move further apart or become free. ▸ The temperature stays the same. |
Energy for a Temperature Rise
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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)
Comparing Internal Energy
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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.
Key Ideas
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.
Key Terms
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Internal energy The total kinetic and potential energy of all the particles in a system. |
Kinetic energy Energy of movement. |
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Potential energy Energy stored because of forces between particles. |
Specific heat capacity Energy needed to raise 1 kg by 1 °C. |
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Temperature A measure of the average kinetic energy of particles. |
System An object or group of objects. |
Your Task: More Energy
10 minutes
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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. |
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.
Can I...?
☐ 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.
Summary
✓ Internal energy = total kinetic + potential energy of the particles.
✓ Heating raises temperature or changes state.
✓ Temperature relates to kinetic energy.
✓ ΔE = mcΔθ.
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EXAM FOCUS What is meant by the internal energy of a system? (2 marks) The total kinetic and potential energy of all the particles. |