# Irreversible Process

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## irreversible process

[‚i·ri′vər·sə·bəl ′prä·səs]
(thermodynamics)
A process which cannot be reversed by an infinitesimal change in external conditions.

## Irreversible Process

a physical process that can occur spontaneously only in one specific direction. Examples of such processes are diffusion, heat conduction, thermal diffusion, viscous flow, and gas expansion into a vacuum. All irreversible processes are nonequilibrium processes. An irreversible process in a closed system is accompanied by an increase in entropy. In open systems, which are capable of exchanging energy or matter with the surrounding medium, during irreversible processes the entropy may remain constant or even decrease owing to entropy exchange with the surrounding medium. In all cases, however, the production of entropy, that is, its increase in the system per unit time, remains positive because of the existence of irreversible processes.

Classical thermodynamics, which studies reversible, equilibrium processes, defines inequalities for irreversible processes; these inequalities determine the possible directions of the irreversible processes.

Irreversible processes are studied through the thermodynamics of nonequilibrium processes and the statistical theory of nonequilibrium processes. The thermodynamics of irreversible processes allows us (1) to obtain the increase of entropy in irreversible processes that occur in various systems as a function of parameters of the nonequilibrium state and (2) to derive equations that describe the time variations of these parameters, for example, diffusion equations, heat-conduction equations, and the Navier-Stokes equation for the hydrodynamics of a viscous fluid. The coefficients in these equations (kinetic coefficients) are regarded as phenomenological constants to be determined experimentally. The statistical theory of irreversible processes makes it possible to obtain expressions for the kinetic coefficients in terms of the molecular constants. Irreversible processes in gases have been studied most completely using the Boltzmann kinetic equation.

D. N. ZUBAREV

References in periodicals archive ?
The book, therefore, makes a valuable and important contribution to the debate on secularization through a comparative analysis of the two different secularization patterns and transformation of church-state relations in Poland and Russia after the 1990s, and reveals that secularization process is not a universal irreversible process but something specific to a certain period of the European history.
In his address at the panel discussion entitled "The Challenges of the European Union in Southeast Europe," Minister Poposki stressed that the integration of the countries of the region into the European Union was an irreversible process and that the process of enlargement had to maintain its credibility with an appropriate and just evaluation of the individual achievements of every country.
I hope we'll see all the elements come into place and make it an irreversible process that can move forward.
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Ashraf Ghani, the head of Afghan Transition, said the security responsibility handover marked "a full and irreversible process which is in action now.
What is clear is that an irreversible process of democratization began in the region, Gul stressed.
This is an irreversible process supported by the great majority of the peoples around the world.
In 1999 Bromberg took the plunge by putting the film stock through a chemical process to re-soften it -an irreversible process which can take up to two years.
In 1999 Bromberg took the plunge by putting the film stock through a chemical process to re-soften it -- an irreversible process which can take up to two years.
We need to enforce achieved accomplishments to make building of parliamentary democracy irreversible process," the head of state said.

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