Carnot cycle

Definition

The Carnot cycle is a theoretical thermodynamic cycle that provides the maximum possible efficiency for a heat engine operating between two temperature reservoirs. It consists of two isothermal processes and two adiabatic processes.

5 Must Know Facts For Your Next Test

1. The Carnot cycle consists of four stages: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression.
2. Efficiency of the Carnot cycle depends only on the temperatures of the hot and cold reservoirs: $\eta = 1 - \frac{T_{cold}}{T_{hot}}$.
3. No real engine can be more efficient than a Carnot engine operating between the same temperatures.
4. The work done by a Carnot engine in one complete cycle is equal to the area enclosed by the cycle on a PV diagram.
5. During the isothermal processes, heat exchange occurs without changing temperature; during adiabatic processes, no heat exchange occurs.

Review Questions

• What are the four stages of the Carnot cycle?
• How do you calculate the efficiency of a Carnot engine?
• Why can't any real engine be more efficient than a Carnot engine?

Related terms

Isothermal Process: A process in which the temperature remains constant while heat may be transferred into or out of the system.

Adiabatic Process: A process in which no heat is transferred to or from the system. All changes in internal energy are due to work done on or by the system.

Second Law of Thermodynamics: A fundamental principle stating that total entropy can never decrease over time for an isolated system; it also implies that perpetual motion machines are impossible.