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Encyclopedia > Thermodynamic equilibrium

In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. The local state of a system at thermodynamic equilibrium is determined by the values of its intensive parameters, as pressure, temperature, etc. Specifically, thermodynamic equilibrium is characterized by the minimum of a thermodynamic potential, such as the Helmholtz free energy, i.e. systems at constant temperature and volume: Thermodynamics (from the Greek Î¸ÎµÏÎ¼Î·, therme, meaning heat and Î´Ï…Î½Î±Î¼Î¹Ï‚, dunamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... Thermodynamics (from the Greek Î¸ÎµÏÎ¼Î·, therme, meaning heat and Î´Ï…Î½Î±Î¼Î¹Ï‚, dunamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... A standard definition of mechanical equilibrium is: A system is in mechanical equilibrium when the sum of the forces, and torque, on each particle of the system is zero. ... Chemical equilibrium is the state in which the concentrations of the reactants and products have no net change over time. ... Thermodynamics (Greek: thermos = heat and dynamic = change) is the physics of energy, heat, work, entropy and the spontaneity of processes. ... It has been suggested that this article or section be merged into intensive and extensive properties. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia. ... Fig. ... In thermodynamics, four quantities, measured in units of energy, are called thermodynamic potentials: where T = temperature, S = entropy, p = pressure, V = volume Differential definitions The following differential relations hold for the four potentials: If we write the above four equations generally as Then it is seen that yielding expressions for... In thermodynamics, the Helmholtz free energy is a thermodynamic potential which measures the â€œusefulâ€ work obtainable from a closed thermodynamic system at a constant temperature. ...

A = U – TS

Or as the Gibbs free energy, i.e. systems at constant pressure and temperature: In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature and pressure. ...

G = H – TS

The process that leads to a thermodynamic equilibrium is called thermalization. An example of this is a system of interacting particles that is left undisturbed by outside influences. By interacting, they will share energy/momentum among themselves and reach a state where the global statistics are unchanging in time. In physics, thermalisation (in American English thermalization) is the process of particles reaching thermal equilibrium through mutual interaction. ... In classical mechanics, momentum (pl. ...

Thermal equilibrium is achieved when two systems in thermal contact with each other cease to exchange energy by heat. If two systems are in thermal equilibrium their temperatures are the same. In thermodynamics, a thermodynamic system is said to be in thermal contact with another system if it can exchange energy with it through the process of heat. ...

Thermodynamics deals with equilibrium states. The word equilibrium implies a state of balance. In an equilibrium state, there are no unbalanced potentials (or driving forces) with the system. A system that is in equilibrium experiences no changes when it is isolated from its surroundings.

The opposite of equilibrium systems are nonequilibrium systems that are instantaneously of balance. Non-equilibrium thermodynamics is a branch of thermodynamics concerned with studying time-dependent thermodynamic systems, irreversible transformations and open systems. ...

• Two systems are in thermal equilibrium when their temperatures are the same.
• Two systems are in mechanical equilibrium when their pressures are the same.
• Two systems are in diffusive equilibrium when their chemical potentials are the same.

Fig. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia. ... In thermodynamics and chemistry, chemical potential, symbolized by Î¼, is a term introduced in 1876 by the American mathematical physicist Willard Gibbs, which he defined as follows: Gibbs noted also that for the purposes of this definition, any chemical element or combination of elements in given proportions may be considered a...

## Conditions for equilibrium

• For a completely isolated system, ΔS = 0 at equilibrium.
• For a system at constant temperature and volume, ΔA = 0 at equilibrium.
• For a system at constant temperature and pressure, ΔG = 0 at equilibrium.

These relationships can be derived by considering the differential form of thermodynamic potentials. This article needs to be cleaned up to conform to a higher standard of quality. ...

## Thermal equilibrium

Thermal equilibrium is when a system's macroscopic thermal observables have ceased to change with time. For example, an ideal gas whose distribution function has stabilised to a specific Maxwell-Boltzmann distribution would be in thermal equilibrium. This outcome allows a single temperature and pressure to be attributed to the whole system. Thermal equilibrium of a system does not imply absolute uniformity within a system; for example, a river system can be in thermal equilbrium when the macroscopic temperature distribution is stable and not changing in time, even though the spatial temperature distribution reflects thermal pollution inputs and thermal dispersion.[1] Macroscopic is commonly used to describe physical objects that are measurable and observable by the naked eye. ... An ideal gas or perfect gas is a hypothetical gas consisting of identical particles of zero volume, with no intermolecular forces. ... In physics, a particles distribution function is a function of seven variables, , which gives the number of particles per unit volume in phase space. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Fig. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia. ... This bridge across the Danube River links Hungary with Slovakia. ... Thermal pollution is a temperature change in natural water bodies caused by human influence. ...

## Local thermodynamic equilibrium

It is useful to distinguish between global and local thermodynamic equilibrium. In thermodynamics, exchanges within a system and between the system and the outside are controlled by intensive parameters. As an example, temperature controls heat exchanges. Global thermodynamic equilibrium (GTE) means that those intensive parameters are homogeneous throughout the whole system, while local thermodynamic equilibrium (LTE) means that those intensive parameters are varying in space and time, but are varying so slowly that for any point, one can assume thermodynamic equilibrium in some neighborhood about that point. It has been suggested that this article or section be merged into intensive and extensive properties. ... Fig. ... The heat equation is an important partial differential equation which describes the variation of temperature in a given region over time. ... It has been suggested that this article or section be merged into intensive and extensive properties. ...

If the description of the system requires variations in the intensive parameters that are too large, the very assumptions upon which the definitions of these intensive parameters are based will break down, and the system will be in neither global nor local equilibrium. For example, it takes a certain number of collisions for a particle to equilibrate to its surroundings. If the average distance it has moved during these collisions removes it from the neighborhood it is equilibrating to, it will never equilibrate, and there will be no LTE. Temperature is, by definition, proportional to the average internal energy of an equilibrated neighborhood. Since there is no equilibrated neighborhood, the very concept of temperature breaks down, and the temperature becomes undefined.

It is important to note that this local equilibrium applies only to massive particles. In a radiating gas, the photons being emitted and absorbed by the gas need not be in thermodynamic equilibrium with each other or with the massive particles of the gas in order for LTE to exist. Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... Radiation as used in physics, is energy in the form of waves or moving subatomic particles. ... The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, infrared radiation, microwaves, radio waves, and visible light are all forms of light. ...

As an example, LTE will exist in a glass of water which contains a melting ice cube. The temperature inside the glass can be defined at any point, but it is colder near the ice cube than far away from it. If energies of the molecules located near a given point are observed, they will be distributed according to the Maxwell-Boltzmann distribution for a certain temperature. If the energies of the molecules located near another point are observed, they will be distributed according to the Maxwell-Boltzmann distribution for another temperature. The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...

Local thermodynamic equilibrium is not a stable state, unless it is maintained by exchanges between the system and the outside. For example, it could be maintained inside the glass of water by regularly adding ice into it in order to compensate for the melting. Transport phenomena are processes which lead a system from local to global thermodynamic equilibrium. Going back to our example, the diffusion of heat will lead our glass of water toward global thermodynamic equilibrium, a state in which the temperature of the glass is completely homogeneous. (Griem 2005) The first edition of Transport Phenomena was published in 1960, two years after having been preliminarily published under the title Notes on Transport Phenomena based on mimeographed notes prepared for a chemical engineering course taught at the University of Wisconsin during the academic year 1957-1958. ... This article or section does not cite any references or sources. ... In physics, heat, symbolized by Q, is defined as transfer of thermal energy [1] Generally, heat is a form of energy transfer associated with the different motions of atoms, molecules and other particles that comprise matter when it is hot and when it is cold. ...

## General references

• Mandl, F. (1988). Statistical Physics, Second Edition, John Wiley & Sons.
•  Griem, Hans R. (2005). Principles of Plasma Spectroscopy (Cambridge Monographs on Plasma Physics). New York: Cambridge University Press.

## Footnotes

1. ^ C.Michael Hogan, Leda C. Patmore and Harry Seidman, Statistical Prediction of Dynamic Thermal Equilibrium Temperatures using Standard Meteorological Data Bases, U.S. Environmental Protection Agency Office of Research and Development EPA-660/2-73-003, August, 1973

A graph of a Normal bell curve showing statistics used in educational assessment and comparing various grading methods. ... In thermodynamics, a thermodynamic system is in thermodynamic equilibrium if its energy distribution equals a Maxwell-Boltzmann-distribution. ... EPA redirects here. ...

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 CiteULike: Equilibrium thermodynamics of homopolymers and clusters: Molecular dynamics and Monte Carlo simulations of ... (507 words) Equilibrium thermodynamics of homopolymers and clusters: Molecular dynamics and Monte Carlo simulations of systems with square-well interactions The thermodynamics of homopolymers and clusters with square-well interactions of up to 64 particles are studied with constant-temperature discontinuous molecular dynamics (DMD) simulations; for comparison Monte Carlo (MC) simulations are also reported. Possible approaches to the experimental observation of the solid-state for an isolated chain are discussed.
 AbeBooks: Suchergebnisse - Adkins und Equilibrium Thermodynamics (1531 words) Although the subject is essentially classical in nature, illustrative material is drawn widely from modern physics and free use is made of microscopic ideas to illuminate it. Equilibrium Thermodynamics gives a comprehensive but concise course in the fundamentals of classical thermodynamics. The terms of reference for Equilibrium Thermodynamics are primarily those of the undergraduate physicist; but it is also suitable for courses in chemistry, engineering, materials science etc. The subject is usually taught in the first or second year of an undergraduate course, but the book takes the student to degree standard (and beyond).
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