# Reversible Process

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## reversible process

[ri′vər·sə·bəl ′prä·səs]
(thermodynamics)
An ideal thermodynamic process which can be exactly reversed by making an indefinitely small change in the external conditions. Also known as quasistatic process.

## Reversible Process

in thermodynamics, any process by which a system passes from one state to another while maintaining the possibility of reverting to the initial state by passing through the same intermediate stages, but in reverse sequence.

In order for a process to be reversible, it must proceed at such a slow rate that it could be considered a continuous series of equilibrium states; in other words, the process must be slow in comparison with the establishment of thermodynamic equilibrium in the given system. Strictly speaking, a reversible process is characterized by an infinitely slow change in the thermodynamic parameters by which equilibrium is defined, for example, density, pressure, and temperature, and thus it is sometimes referred to as a quasistatic process. A quasistatic process is reversible because all of its intermediate states are in thermodynamic equilibrium and thus are insensitive to whether the process proceeds forward or backward.

The first and second laws of thermodynamics are expressed in terms of the concept of the reversible process, which is thus one of the fundamental concepts of macroscopic equilibrium thermodynamics. Natural processes proceed at a finite rate and are accompanied by energy dissipation due to such factors as friction and thermal conductivity: they are therefore called irreversible processes. A reversible process is a theoretical idealization of a natural process that progresses so slowly that any irreversible phenomena can be disregarded.

The microscopic theory of reversible processes is a concern of statistical mechanics.

### REFERENCES

Van der Waals, J. D., and F. Konstamm. Kurs termostatiki, part 1; Obshchaia termostatika. Moscow, 1936. (Translated from German.)
Sommerfeld, A. Termodinamika i statisticheskaia fizika. Moscow, 1955. (Translated from German.)
Leontovich, M. A. Vvedenie v termodinamiku, 2nd ed. Moscow-Leningrad, 1952.
Landau, L. D., and Lifshits, E. M. Statisticheskaia fizika, 2nd ed. (Teoreticheskaia fizika, vol. 5.) Moscow-Leningrad, 1964.
Kubo, R. Termodinamika. Moscow, 1970. (Translated from English.)

D. N. ZUBAREV

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In reversible processes, time appears to be relative.

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