Why can the order of a reaction be detemined from its stoichiometric equation?
The stoichiometric equation has nothing to do with the mechanism of the reaction. There are fast and slow steps to each reaction. The slow steps are the ones that dictate how fast the reaction can proceed because the fast steps will be just waiting around for their chance to react. The stoichiometric equation is just a means of telling the chemist how many moles of reactants they need and what product will evolve. In order to work out the order of a reaction you must have the differential rate law and know that it is an elementary step. Or use experimentation of course :).
