AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Internal energy: Internal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system.
Internal energy is the total energy stored by all the particles in a system.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Internal energy is the total energy stored by all the particles in a system. It is the sum of the kinetic energy of every particle, due to its movement or vibration, and the potential energy of every particle, due to its position and the forces between particles. For example, in a gas, fast-moving particles have high kinetic energy, and particles far apart have high potential energy. Heating transfers energy to the particles, increasing their kinetic or potential energy and so increasing internal energy. Temperature is different: it measures the average kinetic energy of the particles, not the total. A larger mass at the same temperature has more internal energy because there are more particles. Changes of state involve energy transfers that alter potential energy while temperature stays constant.
What earns the marks
- Internal energy is the total kinetic energy plus the total potential energy of all particles in a system.
- Kinetic energy comes from the movement or vibration of particles.
- Potential energy comes from the positions of particles and the forces between them.
- Heating a system increases its internal energy by transferring energy to its particles.
- Temperature is related to average kinetic energy, while internal energy is the total for all particles.
Common mistakes and how to put them right
Writing that internal energy is only kinetic energy.
Put it right: It is the total kinetic energy plus the total potential energy of all particles.
Confusing internal energy with temperature.
Put it right: Temperature is the average kinetic energy per particle, whereas internal energy is the total energy of all particles.
Ignoring mass when comparing internal energies.
Put it right: A larger mass contains more particles, so at the same temperature it has more internal energy.
Exam tips
- Use the phrase 'total kinetic energy and potential energy of all the particles' when defining internal energy.
- Link changes in state to changes in potential energy of particles while temperature remains constant.
- When comparing two systems, refer to both the number of particles and their average kinetic energy.
Try the lesson
The start of the Internal energy: Internal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system. lesson, made from checked teaching notes for this specification point.
Have a go first
Which two types of energy together make up the internal energy of a system?
Listen
Internal energy is the total energy stored by all the particles in a system. It is the sum of the kinetic energy of every particle, due to its movement or vibration, and the potential energy of every particle, due to its position and the forces between particles. For example, in a gas, fast-moving particles have high kinetic energy, and particles far apart have high potential energy. Heating transfers energy to the particles, increasing their kinetic or potential energy and so increasing internal energy. Temperature is different: it measures the average kinetic energy of the particles, not the total. A larger mass at the same temperature has more internal energy because there are more particles. Changes of state involve energy transfers that alter potential energy while temperature stays constant. A strong answer earns marks for these points. Internal energy is the total kinetic energy plus the total potential energy of all particles in a system. Kinetic energy comes from the movement or vibration of particles. Potential energy comes from the positions of particles and the forces between them. Heating a system increases its internal energy by transferring energy to its particles. A common slip: Writing that internal energy is only kinetic energy. Instead, it is the total kinetic energy plus the total potential energy of all particles. Exam tip: Use the phrase 'total kinetic energy and potential energy of all the particles' when defining internal energy.
Key words
Say what each word means before you turn the card.
Internal energy
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Kinetic energy
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Potential energy
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Temperature
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See every definition
- Internal energy
- The total kinetic energy and potential energy of all the particles that make up a system.
- Kinetic energy
- Energy of a particle due to its movement or vibration.
- Potential energy
- Energy of a particle due to its position and the forces between particles.
- Temperature
- A measure of the average kinetic energy of the particles, not the total.
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