The form of the rate constant for elementary reactions at equilibrium   from MD: framework and proposals for thermokinetics
  The rates or formation and concentration distributions of a dimer reaction showing hysteresis behavior are examined in an ab initio chemical reaction designed as elementary and where the hysteresis structure precludes the formation of transition states (TS) with pre-equilibrium and internal sub-reactions. It was discovered that the the reactivity coefficients, defined as a measure of departure from the zero density rate constant for the forward and backward steps had a ratio that was equal to the activity coefficient ratio for the product and reactant species. From the above observations, a theory is developed with the aid of some proven elementary theorems in thermodynamics, and expressions are derived whereby a feasible experimental and computational method for determining the activity coefficients from the rate constants may be obtained The theory developed is applied to ionic reactions where the standard Bronsted-Bjerrum rate equation and exceptions to this are rationalized, and by viewing ion association as a n-meric process, ion activity coefficients may in principle be determined under varying applicable assumptions. 
Christopher G. Jesudason