The reaction mechanism includes reactions with the reaction rate constants k r > 0 . For each r the following notations are used: k r + = k r ; w r + = w r ; k r − − is the reaction rate constant for the reverse reaction if it is in the reaction mechanism and 0 if it is not; w r − − is the reaction rate for the reverse reaction if it is in the reaction mechanism and 0 if it is not. For a reversible reaction, K r = k r + / k r − − is the equilibrium constant.