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# 6: Applications of Thermodynamics


• 6.1: More Processes
When it comes to applications, we need to address processes that are repeated over and over.  To do this, the system must always return to the same starting state, which means that a series of processes must complete a closed cycle.
• 6.2: Engines and Thermal Efficiency
Engines convert heat transfer between two thermal reservoirs at different temperatures into work.  For reasons we will learn later, they are not able to convert all of the heat energy into work, which means that no matter how well-designed they are, they cannot be 100% efficient.  We will examine how these engines work, and define a quantity that measures their efficiency.
• 6.3: Entropy
An imbalance in pressure changes the volume of a system, resulting in work energy entering or exiting the system.  An imbalance of temperature results in heat energy entering or exiting a system, but what is the state variable (analogous to volume) that this imbalance changes?
• 6.4: The Second Law of Thermodynamics
The one-way journey of closed systems from order to disorder, limitations of the thermal efficiency of engines, and the impossibility of a perpetual motion machine are all consequences of one of the most important and misunderstood laws in all of physics.

6: Applications of Thermodynamics is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Tom Weideman directly on the LibreTexts platform.