The actual chemical examples that have been discovered so far have a different mechanism, as we shall see. The concentration of A is held constant by supplying it to the reaction vessel as needed. Note that we are considering a steady-state conhition, which is maintained by the flow of A into the reactor. The periodic variation of the concentrations of the intermediates can be explained as follows. At some stage there may be only a little X present, but Fig.
Some oscillating reactions approach a closed trajectory whatever their starting conditions.
The closed trajectory is called a 'limit cycle'. As less Y becomes available to remove X, X has a chance to surge forward again, and so on. These two concentrations may be calculated by solving the rate equations numerically, and the results are plotted in Fig. The interesting feature is that whatever the initial concentrations of X and Y, the system settles down into the same periodic variation of concentrations. The common trajectory is called a limit cycle, and its period depends on the values of the rate coefficients.