Chemical Kinetics and\nMass Action in Coexisting Phases

The kinetics of chemical reactions are determined by\nthe law of\nmass action, which has been successfully applied to homogeneous, dilute\nmixtures. At nondilute conditions, interactions among the components\ncan give rise to coexisting phases, which can significantly alter\nthe kinetics of chemical reactions. Here, we derive a theory for chemical\nreactions in coexisting phases at phase equilibrium. We show that\nphase equilibrium couples the rates of chemical reactions of components\nwith their diffusive exchanges between the phases. Strikingly, the\nchemical relaxation kinetics can be represented as a flow along the\nphase equilibrium line in the phase diagram. A key finding of our\ntheory is that differences in reaction rates between coexisting phases\nstem solely from phase-dependent reaction rate coefficients. Our theory\nis key to interpreting how concentration levels of reactive components\nin condensed phases control chemical reaction rates in synthetic and\nbiological systems.