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Physics LibreTexts

15: Thermodynamics

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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.

  • 15.0: Prelude to Thermodynamics
  • 15.1: 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
  • 15.2: The First Law of Thermodynamics and Some Simple Processes
    One of the most important things we can do with heat transfer is to use it to do work for us. Such a device is called a heat engine. Car engines and steam turbines that generate electricity are examples of heat engines.
  • 15.3: 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
  • 15.4: 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.
  • 15.5: 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.
  • 15.6: Entropy and the Second Law of Thermodynamics- Disorder and the Unavailability of Energy
  • 15.7: Statistical Interpretation of Entropy and the Second Law of Thermodynamics- The Underlying Explanation
    Disorder is far more likely than order, which can be seen statistically. The entropy of a system in a given state (a macrostate) can be written as s = KLNw, where k = 1.38 \times 10^{-23} \space J/K is Boltzmann’s constant, and lnW is the natural logarithm of the number of microstates W corresponding to the given macrostate.
  • 15.E: Heat and Heat Transfer Methods (Exercise)

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.


This page titled 15: Thermodynamics is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by OpenStax via source content that was edited to the style and standards of the LibreTexts platform.

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