A) The reagents are in the same molar proportions as in . In this case the reagents are in stoichiometric proportions, and at the end, only the products will be present.

B) One of the reagents is in default (in less than the stoichiometric molar proportion). The reaction ends when this reagent is consumed. It is named the limiting reagent. At the end, the reaction products and the unreacted reagents that were in excess, will be present.