  This study reveals that Equilibrium Constant Differential Equations (ECDE)
for nanoconfined reactions derived recently in the frameworks of statistical
mechanics are useful in modeling stochastic chemical kinetics. It is assumed
and verified that if the transient value of the nano-reaction quotient is
treated as being an equilibrium constant, the corresponding equilibrium
reaction extent and its fluctuations (the variance function) coincide with the
respective transient values. The ECDE-computed variance function facilitates
the solution of the stochastic kinetics equations (SKE), as is demonstrated for
a stoichiometric exchange reaction. The results obtained by this original
methodology are in full agreement with those provided by the chemical master
equations. Contrary to the commonly used approaches based on the latter and the
Gillespie algorithm, which need a lot of computer memory and are
time-consuming, the proposed SKE-ECDE method requires to solve only the ECDE
and a single stochastic kinetics differential equation.
