Is the order of a complex reaction determined by the slowest step always? Is it so that order of a reaction is determined by rate determining step and since in a complex mechanism, we write elementary steps hence the order should be the molecularity of the rds?

I am slightly confused in this since I saw that in E1CB the molecularity of the rds is 1 but the order of E1CB is 2.

Basically I know order is determined experimentally but for elementary reactions, don't we write order as the sum of stoichiometric coefficients (here I am assuming that it is not a pseudo order reaction and no products are there in the rate expression.)

  • 2
    $\begingroup$ You're confusing two concepts. The order of a reaction is determined by experiment. The rate of the reaction is limited by the slowest elementary step, which has its own molecularity (or order). But this order is not necessarily the same as the overall reaction order. And in fact, if the slow step is not the first step, they're usually different. $\endgroup$ – Zhe Aug 13 '18 at 17:49
  • $\begingroup$ Related: chemistry.stackexchange.com/questions/15974/… $\endgroup$ – Archer Aug 14 '18 at 3:54