Misplaced Pages

This is an old revision of this page, as edited by 86.141.184.234 (talk) at 18:21, 14 December 2005 (→Extended Interpretations). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Thermodynamics
The classical Carnot heat engine
Branches Classical Statistical Chemical Quantum thermodynamics Equilibrium / Non-equilibrium
Laws Zeroth First Second Third
Systems Closed system Open system Isolated system State Equation of state Ideal gas Real gas State of matter Phase (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
System propertiesNote: Conjugate variables in italics Property diagrams Intensive and extensive properties Process functions Work Heat Functions of state Temperature / Entropy (introduction) Pressure / Volume Chemical potential / Particle number Vapor quality Reduced properties
Material properties Property databases Specific heat capacity  ${\displaystyle c=}$ ${\displaystyle T}$ ${\displaystyle \partial S}$ ${\displaystyle N}$ ${\displaystyle \partial T}$ Compressibility  ${\displaystyle \beta =-}$ ${\displaystyle 1}$ ${\displaystyle \partial V}$ ${\displaystyle V}$ ${\displaystyle \partial p}$ Thermal expansion  ${\displaystyle \alpha =}$ ${\displaystyle 1}$ ${\displaystyle \partial V}$ ${\displaystyle V}$ ${\displaystyle \partial T}$
Equations Carnot's theorem Clausius theorem Fundamental relation Ideal gas law Maxwell relations Onsager reciprocal relations Bridgman's equations Table of thermodynamic equations
Potentials Free energy Free entropy Internal energy ${\displaystyle U(S,V)}$ Enthalpy ${\displaystyle H(S,p)=U+pV}$ Helmholtz free energy ${\displaystyle A(T,V)=U-TS}$ Gibbs free energy ${\displaystyle G(T,p)=H-TS}$
History Culture History General Entropy Gas laws "Perpetual motion" machines Philosophy Entropy and time Entropy and life Brownian ratchet Maxwell's demon Heat death paradox Loschmidt's paradox Synergetics Theories Caloric theory Vis viva ("living force") Mechanical equivalent of heat Motive power Key publications An Inquiry Concerning the Source ... Friction On the Equilibrium of Heterogeneous Substances Reflections on the Motive Power of Fire Timelines Thermodynamics Heat engines Art Education Maxwell's thermodynamic surface Entropy as energy dispersal
Scientists Bernoulli Boltzmann Bridgman Carathéodory Carnot Clapeyron Clausius de Donder Duhem Gibbs von Helmholtz Joule Kelvin Lewis Massieu Maxwell von Mayer Nernst Onsager Planck Rankine Smeaton Stahl Tait Thompson van der Waals Waterston
Other Nucleation Self-assembly Self-organization Order and disorder
Category
v t e

The laws of thermodynamics in principle describe the specifics for the transport of heat and work in thermodynamic processes. Since their conception, however, these laws have become some of the most important in all of physics and many other branches of science. They are often associated with concepts far beyond what is directly stated in the wording.

Zeroth law

If systems A and B are in thermodynamic equilibrium, and systems B and C are in thermodynamic equilibrium, then systems A and C are also in thermodynamic equilibrium.

When two systems are put in contact with each other, there will be a net exchange of energy and/or matter between them unless they are in thermodynamic equilibrium. While this is a fundamental concept of thermodynamics, the need to state it explicitly as a law was not perceived until the first third of the 20th century, long after the first three laws were already widely in use, hence the zero numbering.

Thermodynamic equilibrium includes thermal equilibrium (associated to heat exchange and parameterized by temperature), mechanical equilibrium (associated to work exchange and parameterized generalized forces such as pressure), and chemical equilibrium (associated to matter exchange and parameterized by chemical potential).

First law

The increase in the internal energy of a system is equal to the amount of energy added by heating the system, minus the amount lost as a result of the work done by the system on its surroundings.

This is the statement of the conservation of energy for a thermodynamic system. It refers to the two main ways that a system transfers energy between itself and its surroundings - by the process of heating (or cooling) and the process of mechanical work. The rate of gain or loss in the internal, or stored, energy of a system is determined by the rates of these two processes. In fact, these are only the two most well known processes. Other processes (e.g. adding more particles) may contribute to the gain or loss of internal energy, and for these cases, extra terms must be included in the expression of the first law.

A second aspect of the first law is to clarify the nature of the internal energy. It is a stored quantity. The amount does not depend on which processes put it there. More generally, the amount is independent of the history of the system. If a thermodynamic system goes through changes, becoming warmer, cooler, larger, smaller, whatever, but returns to its original state, then it will have the same amount of internal energy as it did to begin with. Mathematically speaking, the internal energy is a state function and infinitesimal changes in the internal energy are exact differentials.

Second law

It is impossible to obtain a process that, operating in cycle, produces no other effect than the subtraction of a positive amount of heat from a reservoir and the production of an equal amount of work. (the so-called Kelvin-Planck Statement)

The entropy of a thermally isolated macroscopic system never decreases (see Maxwell's demon), however a microscopic system may exhibit fluctuations of entropy opposite to that dictated by the second law (see Fluctuation Theorem). In fact the mathematical proof of the Fluctuation Theorem from time-reversible dynamics and the Axiom of Causality, constitutes a proof of the Second Law. In a logical sense the Second Law thus ceases to be a "Law" of Physics and instead becomes a theorem which is valid for large systems or long times.

Third law

As temperature goes to absolute 0, the entropy of a system approaches a constant.

It is important to remember that, except for the first law, the laws of thermodynamics are only statistical generalizations. That is, they simply describe the tendencies of macroscopic systems. For microsopic systems with few particles, the variations in the parameters become larger than the parameters themselves, and the assumptions of thermodynamics become meaningless. The first law of thermodynamics, however, i.e. the law of conservation, has become the most sound of all laws in science. Its validity has never been disproved.

Extended Interpretations

The laws of thermodynamics are sometimes interpreted to have a wider significance and implication than simply encoding the experimental results upon which the science of thermodynamics is based. See for example:

• Principles of energetics
• Heat death

See also

• Conservation law
• Philosophy of thermal and statistical physics
• Thermodynamics

External links

• 10+ Variations of the 0th Law
• 30+ Variations of the 1st Law
• 110+ Variations of the 2nd Law
• 20+ Variations of the 3rd Law
• 10+ Variations of the 4th Law

• Laws of thermodynamics
• Thermodynamics