Question

Given the equation 4Al + 3O2 -> 2Al2O3 , which reactant is limiting if 0.32 mol Al and 0.26 mol O2 are availiable?

Apparently the limiting reactant is Al, but I don't understand why. Can someone help me understand why Al is the limiting reactant here?

Answer 1

Al is the limiting reagent.

Explanation:

The stoichiometry of the reaction is such that 4 moles of Al are required for every 3 moles of diatomic oxygen. This means that if the ratio of Al to diatomic oxygen is greater than 4/3, then the oxygen is the limiting reagent. If the ratio of Al to diatomic oxygen is less than 4/3, then Al is the limiting reagent.

The problem state that the ratio of Al to diatomic oxygen is

`0.32/0.26=16/13=48/39<52/39=4/3`

The ration of Al to diatomic oxygen is less than 4/3, so Al is the limiting reagent.

We can also see this if we ask the question "How much Aluminum" is required to completely react 0.26 moles of diatomic oxygen??

`0.26cancel(" moles "O_2)xx(4" moles "Al)/(3cancel(" moles "O_2))~~0.347" moles " Al`

So it would take 0.347 moles of Al to completely react with all of the oxygen, however there is only 0.32 moles of Aluminum present, so there is not enough Al to react with all of the oxygen, and so we say that the Al is the limiting reagent.