Classical thermodynamics, heat transfer Definition

Reversible process

Builds on Thermodynamic system Quasistatic process

Definition

Let $\Sigma$ be a thermodynamic system and let $P$ be a process of $\Sigma$ from a state $A$ to a state $B$ . $P$ is reversible if there is a process from $B$ back to $A$ that restores both $\Sigma$ and its surroundings to their initial states. Equivalently, the direction of $P$ can be reversed at every moment by an infinitesimal change of the external conditions.

Remarks

Every reversible process is quasistatic and free of dissipation. The slow, frictionless isothermal expansion of an ideal gas in contact with a reservoir at its own temperature is reversible. Running it backwards compresses the gas, and the heat taken from the reservoir goes back to it. Heat flow from a body at $350$ K to a body at $300$ K is not reversible. No process restores both bodies without leaving a change elsewhere, by the second law. In a reversible process the total entropy of the system and its surroundings stays constant.

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Tag	`YQB46CZFFE`
URI	`m2://YQB46CZFFE`
Kind	definition
Writing	W0 stub
MSC	80A05, 80A10
Defines	Reversible process
Uses	Thermodynamic system, Quasistatic process
Changed	3 November 2026

Reversible process

Definition

Remarks

Reading path

Further reading

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