Why can we not determine the order of a rection by taking into consideration the balanced chemical equation ?

Explanation

The sum of the stoichometric coefficients of the reacting species in a balanced chemical equation may or may not represent its order. This is possible only for elementary reactions which proceeds in single step. In multiple step reactions, the coefficients of the reacting species involved in the rate law determine the order of the reaction. For example, let us consider the following reaction
`KClO_(3) to 6FeSO_(4) to KCl + 3Fe_(2)(SO_(4))_(3) + 3H_(2)O`
The sum of the stoichiometric coefficients in this reaction is ten. But the reactions has been found to be of second order. This means that it is a multistep reaction and in the slowest or the rate determining step the sum of the coefficients of the reacting species involved is only two.