Nonreversible

Nonreversible is an adjective used to describe a process, transformation, or state that cannot be returned to its initial condition by simply reversing the steps or conditions that produced it. In many scientific disciplines, the preferred term is irreversible; “nonreversible” is common in general or informal language and can be used when reversibility is negated without invoking a specific physical law.

In thermodynamics, nonreversible (often called irreversible) processes generate entropy and involve dissipative effects such as friction, internal damping, or diffusive mixing. Because of these losses, the exact initial state cannot be restored without external intervention or additional energy inputs. Idealized models of heat exchange or quasi-static work aim for reversibility, but true thermodynamic reversibility is unattainable in real systems.

In chemistry and materials science, a nonreversible reaction or transformation proceeds predominantly in one direction under given conditions, with products not readily converted back to reactants. Examples include combustion or many hydrolysis reactions. Some phase transformations, welds or microstructural changes are effectively nonreversible, producing lasting alterations in material properties even after external conditions are reversed.

In information theory and computation, processes that lose information in the transformation are effectively irreversible. Landauer's principle links logical irreversibility to minimum energy dissipation; reversible computing aims to minimize such losses by preserving information.

Nonreversible is used across disciplines, but many writers prefer irreversible when describing fundamental constraints. Nonreversible remains common in general language, informal contexts, and in cases where a non-reverting state is emphasized without reference to a governing law.