My textbook Chemistry Part 1,as in the attached photo states that[after the KClO3 reaction] “This reaction which apparently seems to be of the tenth order is actually a second order reaction. This shows that it takes place in several steps.” If that is so, then as stated above it, all higher order inorganic chemistry reactions must have some sort of mechanism. But it is really hard to find the mechanisms(many a times one cannot find them). Why is that so??.enter image description here


Reactions can be of order $0, 1 , 2$ or $3$ , but never more. No collision may happen between more than three particules simultaneously. If an equation is written with more than $4$ substances on the lefthand side, it means that the corresponding reaction is a sum of several elementary reactions.

Mechanisms in inorganic reactions are hard to establish because they are made of a lot of successive reactions, in cascade. And each step is so quick that it cannot be studied. For example your oxidation of $\ce{Fe^{2+}}$ ion by $\ce{KClO3}$ is probably a series of at least $6$ steps which are all nearly instantaneous : To be able to study such a mechanism, the $6$ intermediate states must be observed for at least some nanoseconds. If the intermediate states are too short living, all we can do then is to make hypothesis without experimental arguments.

  • 4
    $\begingroup$ Occasionally fractional, mixed, or negative; for once in a while I prefer the nit-pick global order of reaction vs. order with respect to a substance, too. $\endgroup$
    – Buttonwood
    Mar 26 at 11:56
  • $\begingroup$ One might add that 3rd order reactions are extremely rare. $\endgroup$
    – Karl
    Mar 26 at 17:03
  • 1
    $\begingroup$ @Karl Not as rare, as one could think. Especially when hydrogen bonds or other strong intermolecular interactions are involved. $\endgroup$
    – Mithoron
    Mar 26 at 18:46

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