Limiting Reactants

When reactants are mixed, they are seldom added in the exact stoichiometric proportions as shown
in the balanced equation. Therefore, in most reactions, one of the reactants will be used up first.
This reactant is known as the limiting reactant (or limiting reagent) because it limits the amount of
product that can be formed in the reaction. The reactant that remains after all of the limiting
reactant is used up is called the excess reactant.

TEST STRATEGY

If  the quantities  of  two reactants   are given,  be  on  the lookout for the possibility that    one of

them    is  a   limiting    reactant.

Example: If 28  g   of  Fe  reacts  with    24  g   of  S   to  produce FeS,    what    would   be  the limiting

reactant?   How many    grams   of  excess  reactant    would   be  present in  the vessel  at  the

end of  the reaction?

Solution: First,    the balanced    equation    needs   to  be  determined. We  are told    that    Fe  and S

come    together    to  form    FeS:

Fe  +   S   →   FeS

This    is  already balanced.

Next,   the number  of  moles   for each    reactant    must    be  determined.