reversible

Reversible is an adjective used to describe something that can be turned back to its original form, state, or condition. In science and engineering, it often refers to processes or reactions that can proceed in both directions, allowing the system to be restored to its initial state without lasting change.

In thermodynamics, a reversible process is an idealized, quasi-static change in which the system and surroundings can be returned to their starting conditions with no net change in entropy. Real processes are irreversible, typically due to friction, dissipative effects, finite temperature differences, or mixing, and they incur entropy production and energy losses. Reversible processes are used as a theoretical standard that defines the upper limit of efficiency for heat engines.

In chemistry, a reversible reaction (also called an equilibrium reaction) allows reactants to form products and products to revert to reactants. The mixture reaches a dynamic balance where both directions occur simultaneously, with the relative amounts determined by temperature, pressure, and concentrations. The concept is described by equilibrium constants and Le Chatelier’s principle.

In computing and information theory, reversible computing refers to computational processes that preserve information, meaning each output state maps uniquely to an input state. Such processes can, in principle, be run backward to recover inputs, and they are studied for potential energy efficiency benefits. Quantum computing, where operations are typically reversible, is closely related to this idea.

Reversibility also appears in everyday usage, such as clothing or items designed to be worn or used with two sides or orientations available, effectively providing two styles in one object.