Physical changes, such as phase transitions, are also reversible and may establish equilibrium. As one example, consider the vaporization of bromine:

Br_2(l) ⇌ Br_2(g)

When liquid bromine added to an otherwise empty container and then seal the container, the forward process depicted above (vaporization) will commence and continue at a roughly constant rate as long as the exposed surface area of the liquid, so its temperature remains constant. As increasing amounts of gaseous bromine produced, the rate of the reverse process (condensation) will increase until it equals the rate of vaporization, and the equilibrium established.