12: Thermodynamics
Thermodynamics is the branch of science concerned with heat and temperature and their relation to energy and work. It states that the behavior of these quantities is governed by the four laws of thermodynamics, irrespective of the composition or specific properties of the material or system in question. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, chemical engineering, and mechanical engineering.
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- 12.2: The First Law of Thermodynamics
- The first law of thermodynamics is given as \(\Delta U = Q - W\), where \(\Delta U\) is the change in internal energy of a system, \(Q\) is the net heat transfer (the sum of all heat transfer into and out of the system), and \(W\) is the net work done (the sum of all work done on or by the system). Both \(Q\) and \(W\) are energy in transit; only \(\Delta U\) represents an independent quantity capable of being stored. The internal energy \(U\) of a system depends only on the state of the system
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- 12.4: Introduction to the Second Law of Thermodynamics - Heat Engines and their Efficiency
- The two expressions of the second law of thermodynamics are: (i) Heat transfer occurs spontaneously from higher- to lower-temperature bodies but never spontaneously in the reverse direction; and (ii) It is impossible in any system for heat transfer from a reservoir to completely convert to work in a cyclical process in which the system returns to its initial state. Irreversible processes depend on path and do not return to their original state. Cyclical processes are processes that return to the
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- 12.5: Carnot’s Perfect Heat Engine- The Second Law of Thermodynamics Restated
- A Carnot engine operating between two given temperatures has the greatest possible efficiency of any heat engine operating between these two temperatures. Furthermore, all engines employing only reversible processes have this same maximum efficiency when operating between the same given temperatures. The second law of thermodynamics can be restated in terms of the Carnot cycle, and so what Carnot actually discovered was this fundamental law.
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- 12.6: Applications of Thermodynamics- Heat Pumps and Refrigerators
- An artifact of the second law of thermodynamics is the ability to heat an interior space using a heat pump. Heat pumps compress cold ambient air and, in so doing, heat it to room temperature without violation of conservation principles. To calculate the heat pump’s coefficient of performance, use the equation \(COP_{hp} = \dfrac{Q_h}{W}\). A refrigerator is a heat pump; it takes warm ambient air and expands it to chill it.
Thumbnail: The Steam engine and gas and oil engines. By John Perry. 1899. This file is in the public domain because its copyright has expired in the United States.
Contributors and Attributions
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Paul Peter Urone (Professor Emeritus at California State University, Sacramento) and Roger Hinrichs (State University of New York, College at Oswego) with Contributing Authors: Kim Dirks (University of Auckland) and Manjula Sharma (University of Sydney). This work is licensed by OpenStax University Physics under a Creative Commons Attribution License (by 4.0) .