Less commonly appreciated, is the possibility of achieving a non-equilibrium steady state by mechanistically 7 coupling a reaction network to a second spontaneous process. If the components of the coupled reaction are "chemostated" away from their equilibrium concentrations, the relative concentrations of some species in the network may be perturbed from the values predicted by the corresponding equilibrium constants and flux can take place through the network (i.e., detailed balance can be broken), which can in principle be harnessed to do useful work. A chemical example of a cyclic equilibrium. c) Kelly's helicene rotor 1 with a ratchet-like potential-energy surface that nonetheless fails to rotate unidirectionally at equilibrium.