Second law of thermodynamics

Definition

The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. It implies that natural processes tend to move towards a state of maximum disorder or entropy.

5 Must Know Facts For Your Next Test

1. Entropy always increases in an isolated system; it never decreases.
2. Heat engines cannot be 100% efficient due to unavoidable entropy production.
3. The second law explains why perpetual motion machines of the second kind are impossible.
4. A heat engine's efficiency is limited by the temperatures of its heat reservoirs, as described by Carnot's theorem.
5. The second law can be restated using Kelvin-Planck and Clausius statements.

Review Questions

• Why can't a heat engine be 100% efficient according to the second law of thermodynamics?
• What does the second law imply about the direction of natural processes?
• How does Carnot's theorem relate to the efficiency of real heat engines?

Related terms

Entropy:

A measure of disorder or randomness in a system.

Heat Engine: A device that converts thermal energy into mechanical work, operating between two heat reservoirs.

Carnot Cycle: An idealized thermodynamic cycle representing the most efficient possible heat engine.