{{thermodynamics, cTopic=Branches Equilibrium Thermodynamics is the systematic study of transformations of matter and energy in systems in terms of a concept called

thermodynamic equilibrium Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermod ...

. The word equilibrium implies a state of balance. Equilibrium thermodynamics, in origins, derives from analysis of the

Carnot cycle A Carnot cycle is an ideal thermodynamic cycle proposed by French physicist Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. By Carnot's theorem, it provides an upper limit on the efficiency of any classical thermodynam ...

. Here, typically a system, as cylinder of gas, initially in its own state of internal thermodynamic equilibrium, is set ''out of balance'' via heat input from a

combustion reaction Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...

. Then, through a series of steps, as the system settles into its final equilibrium state, work is extracted. In an equilibrium state the

potentials Potential generally refers to a currently unrealized ability, in a wide variety of fields from physics to the social sciences. Mathematics and physics * Scalar potential, a scalar field whose gradient is a given vector field * Vector potential ...

, or driving forces, within the system, are in exact balance. A central aim in equilibrium thermodynamics is: given a system in a well-defined initial

state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * ''The State'' (newspaper), a daily newspaper in Columbia, South Carolina, United States * ''Our S ...

, subject to accurately specified constraints, to calculate, when the constraints are changed by an externally imposed intervention, what the state of the system will be once it has reached a new equilibrium. An equilibrium state is mathematically ascertained by seeking the extrema of a thermodynamic potential function, whose nature depends on the constraints imposed on the system. For example, a chemical reaction at constant temperature and pressure will reach equilibrium at a minimum of its components'

Gibbs free energy In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work that may be performed by a thermodynamically closed system at constant temperature and pr ...

and a maximum of their

entropy Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...

. Equilibrium thermodynamics differs from

non-equilibrium thermodynamics Non-equilibrium thermodynamics is a branch of thermodynamics that deals with physical systems that are not in thermodynamic equilibrium but can be described in terms of macroscopic quantities (non-equilibrium state variables) that represent an ext ...

, in that, with the latter, the state of the system under investigation will typically not be uniform but will vary locally in those as energy, entropy, and temperature distributions as gradients are imposed by dissipative thermodynamic fluxes. In equilibrium thermodynamics, by contrast, the state of the system will be considered uniform throughout, defined macroscopically by such quantities as temperature, pressure, or volume. Systems are studied in terms of change from one equilibrium state to another; such a change is called a

thermodynamic process Classical thermodynamics considers three main kinds of thermodynamic process: (1) changes in a system, (2) cycles in a system, and (3) flow processes. (1)A Thermodynamic process is a process in which the thermodynamic state of a system is change ...

Ruppeiner geometry Ruppeiner geometry is thermodynamic geometry (a type of information geometry) using the language of Riemannian geometry to study thermodynamics. George Ruppeiner proposed it in 1979. He claimed that thermodynamic systems can be represented by Rieman ...

is a type of information geometry used to study thermodynamics. It claims that thermodynamic systems can be represented by

Riemannian geometry Riemannian geometry is the branch of differential geometry that studies Riemannian manifolds, smooth manifolds with a ''Riemannian metric'', i.e. with an inner product on the tangent space at each point that varies smoothly from point to poin ...

, and that statistical properties can be derived from the model. This geometrical model is based on the idea that there exist equilibrium states which can be represented by points on two-dimensional surface and the distance between these equilibrium states is related to the fluctuation between them.

References

* Adkins, C.J. (1983). ''Equilibrium Thermodynamics, 3rd Ed''. Cambridge: Cambridge University Press. * Cengel, Y. & Boles, M. (2002). ''Thermodynamics – an Engineering Approach, 4th Ed.'' (textbook). New York: McGraw Hill. * Kondepudi, D. & Prigogine, I. (2004). ''Modern Thermodynamics – From Heat Engines to Dissipative Structures'' (textbook). New York: John Wiley & Sons. * Perrot, P. (1998). ''A to Z of Thermodynamics'' (dictionary). New York: Oxford University Press. Branches of thermodynamics

See also

References