The reaction is assumed to be separated in two phases: an initial fast transient followed by a QSS period. Briefly, after an initial fast transient, the complex c 1 reaches a QSS, and the velocity of its formation is more or less equal to the velocity of its depletion (making ċ1 ≈ 0 for the duration of the QSS phase). Setting ċ1 to 0 in (7b) yields