Entropy

:For other senses of the term entropy, see entropy (disambiguation).

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In thermodynamics and statistical mechanics, the thermodynamic entropy (or simply the entropy) S is a measure of the internal disorder present in a system at thermodynamic equilibrium; or, equivalently, the number of possible internal configurations available to the system. The entropy can also be understood as the "quality" of heat flowing between two bodies. The SI unit of entropy is J?K-1 (joules per kelvin), which is the same as the unit of heat capacity.

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An important and well-known law of physics, known as the second law of thermodynamics, states that the entropy of an isolated system can never decrease. We will explain the meaning of the "second law" in a subsequent section.

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The concept of entropy was originally introduced in 1865 by Rudolf Clausius, in the context of classical thermodynamics. In 1877, Ludwig Boltzmann formulated an alternative definition of entropy as a measure of disorder, which is now regarded as one of the basic postulates of the theory of statistical mechanics. The closely-related concept of information entropy, used in information theory, was introduced by Claude Shannon in 1948.

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Thermodynamics: Thermodynamics (Greek: thermos = heat and dynamis = power) is the physics of heat, work, enthalpy, and entropy changes in relation to the spontaneity of processes. In origins, thermodynamics is the study of engines. Prior to 1698, with the invention of the Savery Engine, horses were used to "power...

Statistical mechanics: Statistical mechanics is the application of statistics, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. It provides a framework for relating the microscopic propert...

Thermodynamic equilibrium: In thermodynamics, a thermodynamic system is in thermodynamic equilibrium if its energy distribution equals a Maxwell-Boltzmann distribution. This allows a single temperature to be attributed to the system. The key idea is that the macroscopic parameters are unchanging. The term "thermal equilibrium...

Entropy related Images and Photos (experimental)

Entropy

Entropy I

Entropy II