Internal energy is the sum of the random kinetic energy and the potential energy of all the particles in a body.
Components
- Kinetic energy of particles: related to temperature. Higher temperature means greater average kinetic energy of particles.
- Potential energy of particles: related to the separation between particles and the forces between them. During a change of state, potential energy changes while kinetic energy (and therefore temperature) stays constant.
How internal energy increases
When a substance is heated:
- If no change of state: the kinetic energy of the particles increases (temperature rises), and the potential energy stays roughly the same.
- During a change of state: the potential energy of the particles increases (bonds are broken), but the kinetic energy stays the same (temperature stays constant).
In exam questions
Distinguish between internal energy and temperature. Temperature is related only to the average kinetic energy of the particles. Internal energy includes both kinetic and potential energy. During melting or boiling, internal energy increases but temperature does not.
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