In contrast to common opinion, it is shown that equilibrium constants
determine the time-dependent behavior of particular ratios of concentrations
for any system of reversible first-order reactions. Indeed, some special ratios
actually coincide with the equilibrium constant at any moment in time. This is
established for batch reactors, and similar relations hold for steady-state
plug-flow reactors, replacing astronomic time by residence time. Such
relationships can be termed time invariants of chemical kinetics