Internal energy

Definition

Internal energy is the total energy contained within a system due to both the random motions of its particles and the potential energies of their interactions. It encompasses kinetic and potential energy at the microscopic level.

5 Must Know Facts For Your Next Test

1. Internal energy increases with temperature as particle motion becomes more vigorous.
2. Work done on or by the system can change its internal energy without altering temperature.
3. Internal energy is a state function, meaning it depends only on the current state of the system, not how it got there.
4. The First Law of Thermodynamics states that the change in internal energy is equal to heat added to the system minus work done by the system: $$\Delta U = Q - W$$.
5. For an ideal gas, internal energy depends only on temperature and not on volume or pressure.

Review Questions

• How does adding heat to a system affect its internal energy?
• What does it mean that internal energy is a state function?
• What is the relationship between internal energy, heat, and work according to the First Law of Thermodynamics?

Related terms

Heat:

Energy transferred between systems or objects due to a temperature difference.

Work:

Energy transfer that occurs when a force is applied over a distance.

Specific Heat:

The amount of heat required to raise the temperature of one unit mass of a substance by one degree Celsius.