The Carnot Cycle and Efficiency

In 1824, a French military engineer named Nicolas Leonard Sadi Carnot (his third name is borrowed from a Persian poet, and his surname is pronounced kar-NO) published an article that ultimately played a major—though roundabout—role in the development of thermodynamics. It was ignored at the time. The first law of thermodynamics had not even been established yet, and heat was still thought of as caloric. It was not until 1848 that Lord Kelvin brought the attention of the scientific world to the work, 16 years after Carnot s early death at age 36. However, the article introduced a lasting concept, the definition of the Carnot cycle. 

Unless otherwise noted, all art on this page is Cengage Learning 2014. 

Reversible adiabatic expansion. In this step, q = 0, but because it is expansion, work is done by the engine. The work is defined as W2. 

Reversible adiabatic compression. The system (that is, the engine) is returned to its original conditions. In this step, q is 0 again, and work is done on the system. This amount of work is termed 1V4. 

Because the system has returned to the original conditions, by definition of a state function, AL7 = 0 for the overall process. By the first law of thermodynamics, 

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