reequilibration

Reequilibration is the process by which a system returns to an equilibrium state after being disturbed. It describes how state variables such as concentrations, temperatures, and pressures adjust toward their equilibrium values under the ambient constraints of temperature, volume, and chemical potentials.

It is characterized by a relaxation dynamic in which the deviation from equilibrium decays over time, often following an exponential form. The characteristic time scale, known as the relaxation time, depends on the mechanisms at work—chemical kinetics, diffusion, heat or mass transfer, and, in multi-phase systems, interfacial transport.

Reequilibration occurs in many contexts. In chemistry, a disrupted solution returns to the equilibrium composition after a perturbation such as addition of a reactant or a change in temperature. In materials science, diffusion and phase changes drive reequilibration after heat treatment. In biology and ecology, perturbations can lead to reequilibration of metabolic fluxes or population densities toward steady-state or equilibrium conditions.

It is distinct from the initial approach to equilibrium in that a perturbation has already displaced the system from its previous state. Analysts describe it using rate equations, linear response theory, and time constants, and consider factors such as catalysts, barriers, transport limitations, and reservoir conditions.

See also equilibrium, relaxation time, Le Chatelier's principle.