AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Internal energy: Heating changes the energy stored within the system by increasing the energy of the particles that make up the system. This either raises the temperature of the system or produces a change of state.
Internal energy is the total energy stored in a system, made up of the kinetic energy of its particles and the potential energy linked to their positions and bonds.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Internal energy is the total energy stored in a system, made up of the kinetic energy of its particles and the potential energy linked to their positions and bonds. Heating transfers energy to the system, so the particles gain energy. That extra energy can be shared out in two ways. If the particles vibrate or move faster, their average kinetic energy rises and the temperature increases. If the energy instead breaks or loosens bonds between particles, the arrangement changes and a change of state occurs, such as melting or boiling, while the temperature stays constant.
For example: Heating ice warms it to 0 °C, then melting absorbs energy without a temperature rise until all the ice has melted.
What earns the marks
- Internal energy is the sum of the kinetic and potential energies of all the particles in a system.
- Heating transfers energy to the particles, increasing the energy stored in the system.
- An increase in the average kinetic energy of the particles raises the temperature of the system.
- Energy used to overcome forces between particles can change the state without changing temperature.
- During a change of state, energy is transferred but the temperature remains constant until the change is complete.
- A temperature rise and a change of state are alternative outcomes of the same energy transfer by heating.
Common mistakes and how to put them right
Saying that heating always raises the temperature.
Put it right by noting that during a change of state the energy goes into breaking bonds, so temperature stays constant.
Confusing temperature with internal energy.
Put it right by explaining that temperature depends on average particle kinetic energy, while internal energy includes potential energy too.
Thinking particles gain energy only by moving faster.
Put it right by stating that energy can also increase the potential energy of particles as bonds are overcome.
Exam tips
- Use the phrase 'energy stored within the system' when defining internal energy, and link it to both kinetic and potential energy of particles.
- When describing a change of state, state clearly that temperature is constant and explain where the transferred energy goes.
- Sketch or describe a heating curve to show a flat section during melting or boiling, labelling the temperature as constant.
Try the lesson
The start of the Internal energy: Heating changes the energy stored within the system by increasing the energy of the particles that make up the system. This either raises the temperature of the system or produces a change of state. lesson, made from checked teaching notes for this specification point.
Have a go first
A sealed pan of water is heated on a hob. The water becomes hotter but does not boil. What does the heating do to the energy stored in the water?
Listen
Internal energy is the total energy stored in a system, made up of the kinetic energy of its particles and the potential energy linked to their positions and bonds. Heating transfers energy to the system, so the particles gain energy. That extra energy can be shared out in two ways. If the particles vibrate or move faster, their average kinetic energy rises and the temperature increases. If the energy instead breaks or loosens bonds between particles, the arrangement changes and a change of state occurs, such as melting or boiling, while the temperature stays constant. For example, heating ice warms it to 0 °C, then melting absorbs energy without a temperature rise until all the ice has melted. A strong answer earns marks for these points. Internal energy is the sum of the kinetic and potential energies of all the particles in a system. Heating transfers energy to the particles, increasing the energy stored in the system. An increase in the average kinetic energy of the particles raises the temperature of the system. Energy used to overcome forces between particles can change the state without changing temperature. A common slip: Saying that heating always raises the temperature. Instead, noting that during a change of state the energy goes into breaking bonds, so temperature stays constant. Exam tip: Use the phrase 'energy stored within the system' when defining internal energy, and link it to both kinetic and potential energy of particles.
Key words
Say what each word means before you turn the card.
Internal energy
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Heating
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Temperature
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Change of state
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See every definition
- Internal energy
- The total energy stored in a system, made up of the kinetic energy of its particles and the potential energy linked to their positions and bonds.
- Heating
- Transfers energy to the system, so the particles gain energy, increasing the energy stored within the system.
- Temperature
- Depends on the average kinetic energy of the particles, so it rises when the particles vibrate or move faster.
- Change of state
- Occurs when energy instead breaks or loosens bonds between particles, so the arrangement changes while the temperature stays constant.
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