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Entropy
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Thermodynamics
The classical Carnot heat engine
Book:Thermodynamics
Classical
Statistical
Chemical
Equilibrium / Non-equilibrium
Zeroth
First
Second
Third
State
Equation of state
Ideal gas
Real gas
Phase / State of matter
Equilibrium
Control volume
Instruments
Processes
Isobaric
Isochoric
Isothermal
Adiabatic
Isentropic
Isenthalpic
Quasistatic
Polytropic
Free expansion
Reversibility
Irreversibility
Endoreversibility
Cycles
Heat engines
Heat pumps
Thermal efficiency
Property diagrams
Intensive and extensive properties
Functions of state
(Conjugate variables in italics)
Temperature / Entropy
Introduction to entropy
Pressure / Volume
Chemical potential / Particle number
Vapor quality
Reduced properties
Process functions
Work
Heat
Specific heat capacity
Compressibility
Thermal expansion
Property database
Carnot's theorem
Clausius theorem
Fundamental relation
Ideal gas law
Maxwell relations
Onsager reciprocal relations
Bridgman's thermodynamic equations
Table of thermodynamic equations
Free energy
Free entropy
Internal energy
Enthalpy
Helmholtz free energy
Gibbs free energy
Philosophy
Entropy and time
Entropy and life
Brownian ratchet
Maxwell's demon
Heat death paradox
Loschmidt's paradox
Synergetics
History
General
Heat
Entropy
Gas laws
"Perpetual motion" machines
Theories
Caloric theory
Vis viva
Theory of heat
Mechanical equivalent of heat
Motive power
Key publications
"An Experimental Enquiry
Concerning ... Heat"
"On the Equilibrium of
Heterogeneous Substances"
"Reflections on the
Motive Power of Fire"
Timelines
Thermodynamics
Heat engines
Art
Maxwell's thermodynamic surface
Education
Entropy as energy dispersal
Bernoulli
Carnot
Clapeyron
Clausius
Carathéodory
Pierre Duhem
Gibbs
von Helmholtz
Joule
Maxwell
von Mayer
Onsager
Rankine
Smeaton
Stahl
Thompson
Thomson (Baron Kelvin)
Waterson
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Entropy articles
Introduction
History
Classical
Statistical
In thermodynamics, entropy (usual symbol S) is a measure of the number of specific ways in which a thermodynamic system may be arranged, often taken to be a measure of disorder, or a measure of progressing towards thermodynamic equilibrium. The entropy of an isolated system never decreases, because isolated systems spontaneously evolve towards thermodynamic equilibrium, which is the state of maximum entropy.The change in entropy (?S) was originally defined for a thermodynamically reversible process as:,which is found from the uniform thermodynamic temperature (T) of a closed system dividing an incremental reversible transfer of heat into that system (dQ). The above definition is sometimes called the macroscopic definition of entropy because it can be used without regard to any microscopic picture of the contents of a system. In thermodynamics, entropy has been found to be more generally useful and it has several other formulations. Entropy was discovered when it was noticed to be a quantity that behaves as a function of state, as a consequence of the second law of thermodynamics. Entropy is an extensive property, but it is often given intensively in the form of specific entropy, the entropy per unit mass, or molar entropy, the entropy per mole.The absolute entropy (S rather than ?S) was defined later, using either statistical mechanics or the third law of thermodynamics.In the modern microscopic interpretation of entropy in statistical mechanics, entropy is the amount of additional information needed to specify the exact physical state of a system, given its thermodynamic specification. Understanding the role of thermodynamic entropy in various processes requires understanding how and why that information changes as the system evolves from its initial condition. It is often said that entropy is an expression of the disorder, or randomness of a system, or of our lack of information about it. The second law is now often seen as an expression of the fundamental postulate of statistical mechanics via the modern definition of entropy.
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