For the reversible reaction A⇌B, the forward step A→B has a rate constant  and the backwards step B→A has a rate constant . The concentration of A obeys the following differential equation:
If we consider that the concentration of product B at anytime is equal to the concentration of reactants at time zero minus the concentration of reactants at time , we can set up the following equation:
Combining  and , we can write
Separation of variables is possible and using an initial value , we obtain:
and after some algebra we arrive at the final kinetic expression:
The concentration of A and B at infinite time has a behavior as follows:
Thus, the formula can be linearized in order to determine :
To find the individual constants  and , the following formula is required: