Kelvin statement of the second law of thermodynamics

Definition

The Kelvin statement of the second law of thermodynamics asserts that it is impossible for any device to operate in a cycle and convert all the heat absorbed from a single thermal reservoir into work, without producing any other effect.

5 Must Know Facts For Your Next Test

1. The Kelvin statement emphasizes the impossibility of a perfect heat engine.
2. It implies that some energy must always be lost as waste heat in practical engines.
3. The statement is equivalent to the Clausius statement when it comes to the principles they express.
4. Any violation of the Kelvin statement would also violate the Clausius statement, demonstrating their equivalence.
5. The Kelvin-Planck form is another name for this statement, often encountered in thermodynamics literature.

Review Questions

• What does the Kelvin statement of the second law of thermodynamics imply about heat engines?
• How does the Kelvin statement relate to the concept of perpetual motion machines?
• Explain why violating the Kelvin statement would also violate the Clausius statement.

Related terms

Second Law of Thermodynamics: A fundamental principle stating that total entropy can never decrease over time for an isolated system, and processes occur in a direction where entropy increases.

Clausius Statement: Another formulation of the second law which states that heat cannot spontaneously flow from a colder body to a hotter body without external work being performed on the system.

Heat Engine: $$A device that converts thermal energy into mechanical work by exploiting temperature differences between heat reservoirs.$$