irreversible process

[‚i·ri′vər·sə·bəl ′prä·səs]

(thermodynamics)

A process which cannot be reversed by an infinitesimal change in external conditions.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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

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References in periodicals archive

Elastic deformation of the blocks and clusters are reversible and do not contribute to the irreversible process. Therefore discrete blocks (in a discrete brittle rock mass) or discrete clusters (in a plastic ground) are the natural components that comprise the ground volume as a thermodynamic system.

CLUSTER BEHAVIOR OF THE GROUND DURING ITS IRREVERSIBLE MOVEMENT

In presence of reaction, we have considered a term characterizing an irreversible process and a boundary condition which can be related to a sorption-desorption process.

Anomalous Diffusion with an Irreversible Linear Reaction and Sorption-Desorption Process

Results depicted in Figure 5(c) show a linear dependence of ln[protein] on [T.sub.m] (0.4 and 0.56 mg x [mL.sup.-1], reversible process) and on apparent [T.sub.m] (0.8 and 1.1 mg x [mL.sup.-1], irreversible process).

Effect of temperature on xylanase II from Trichoderma reesei QM 9414: a calorimetric, catalytic, and conformational study

legislation, that its effective implementation makes Georgia's European integration an irreversible process. This Agreement shifts EU-

Association Agreement to Shift EU-Georgia Relations to a New Level -MFA

Banking union remains "an irreversible process," however, insisted the French president, even if there are still quite a few chapters to be written in the history of building the eurozone.

EUROPEAN COUNCIL : QUESTION OF TRUST

(5) the dimerization is considered as a chemically irreversible process (ErCi formalism).

Calculation of Rate Constant of Dimerization of an Electrochemically Generated Species

Elaborate discussion of these two cases is important, as it allows the reader to question whether secularization is an irreversible process that every society has to go through in the same way, to what extent the experiences of Eastern European societies differ from that of the West in terms of secularization, and whether the revitalization of religion in post-communist societies and easing of tension between the state and religion pose a challenge to the secularization theory and secularization model that was foreseen by the communist regimes.

Religion, Identity and Politics in Russia and Poland/Rusya ve Polonya'da Din, Kimlik, Siyaset

The scientists were looking at a range of platelet function tests such as platelet activation - a reversible process where platelets are starting to get stressed and sticky - and platelet aggregation - an irreversible process when sticky platelets clump together.

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In addition to being an irreversible process that has led to wrongful deaths, she also believes it does not deter criminals and goes against the belief that the "most important human right is the right to life."

Executions in Japan remind leaders of abolition goal: Norway official

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.

Foreign Minister Poposki attends Bled Strategic Forum