What determines how quickly nitrogen tetroxide and nitrogen dioxide return to equilibrium?

The rate at which nitrogen tetroxide and nitrogen dioxide return to chemical equilibrium following a disturbance is determined by the concentrations of the reactants and their specific reactivities.1

Because systems at equilibrium cannot respond instantaneously to changes in external conditions like temperature or pressure, they undergo a process known as chemical relaxation. The speed of this re-equilibration is governed by the probability per unit time that a nitrogen tetroxide molecule will dissociate into two nitrogen dioxide molecules, balanced against the rate at which those monomers recombine to form the dimer.1

The time required for this process is characterized by the relaxation time ($\tau$), which represents the reciprocal of the constant of proportionality in the rate equation governing the system's return to equilibrium. By measuring this relaxation time—often through observing effects like sound absorption or dispersion—scientists can derive the specific rates of both the dissociation and association reactions.21