Internal Energy
Get to grips with Internal Energy for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Internal energy is the total kinetic and potential energy of all the particles in a system, and increases when it is heated.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
The internal energy of a system is the total energy stored by the particles that make it up. It is the sum of their kinetic energy and their potential energy.
Heating a system increases its internal energy. This either raises the temperature, because the particles gain kinetic energy and move faster, or produces a change of state, because the particles gain potential energy as the forces between them are overcome.
During a change of state the temperature does not change, even though energy is still being supplied. This is because the energy goes into breaking the forces between particles rather than making them move faster, which is why heating and cooling graphs have flat sections.
Revision notes
What internal energy is
Internal energy is the total energy stored by the particles making up a system.
It is the sum of the kinetic energy of the particles and the potential energy arising from the forces between them.
Heating and temperature
Heating increases the internal energy of a system.
If the temperature rises, the particles have gained kinetic energy and move faster. The amount of energy needed depends on the mass, the specific heat capacity and the temperature change.
Heating and change of state
During a change of state the temperature stays constant even though energy is still supplied.
The energy goes into increasing the potential energy of the particles, overcoming the forces between them, rather than increasing their kinetic energy. This produces the flat sections on a heating graph.
Key points
- Internal energy is the total energy of the particles.
- It is kinetic plus potential energy.
- Heating increases internal energy.
- A temperature rise means increased kinetic energy.
- A change of state means increased potential energy.
- Temperature stays constant during a change of state.
Worked examples
Example 1
Define internal energy. [2 marks]
Model answer
Internal energy is the total energy stored by the particles making up a system (1 mark), which is the sum of their kinetic energy and their potential energy (1 mark).
Example 2
Explain why the temperature stays constant while ice is melting, even though energy is still being supplied. [3 marks]
Model answer
The energy supplied increases the potential energy of the particles rather than their kinetic energy (1 mark). It is used to overcome the forces holding the particles in their fixed positions (1 mark). Since temperature depends on the kinetic energy of the particles, it does not change (1 mark).
Example 3
Explain what happens to the particles when a substance is heated and its temperature rises. [2 marks]
Model answer
The particles gain kinetic energy (1 mark) and therefore move faster, which is measured as a rise in temperature (1 mark).
Common mistakes
Saying internal energy is just heat.
It is the total kinetic and potential energy of the particles.
Saying temperature rises during a change of state.
It stays constant while the state is changing.
Saying no energy is supplied during melting.
Energy is supplied throughout; it just does not raise the temperature.
Confusing kinetic and potential energy of particles.
Kinetic relates to temperature; potential relates to change of state.
Exam tips
- Define internal energy as kinetic plus potential.
- Explain flat graph sections through potential energy.
- Link temperature specifically to kinetic energy.
- Say the forces between particles are overcome.
Key terms
- Internal energy
- The total kinetic and potential energy of the particles.
- Kinetic energy
- Energy of the particles due to their motion.
- Potential energy
- Energy due to the forces between particles.
- Change of state
- A physical change during which temperature stays constant.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.