Limiting Reagent

Question

1.     Zn + 2HCl ⮕ ZnCl₂ + H₂

a)     How many grams of ZnCl₂ are formed from 150 g of Zn and 73 g of HCl?

b)     Which substance is in excess?

Answer 1

There are several ways to find the limiting reagent. One simple way is to divide the mols of each reagent by the corresponding coefficient in the balanced equation and whichever value is less, that identifies the limiting reagent.

Zn + 2HCl ==> ZnCl2 + H2 ... BALANCED EQUATION

for Zn we have: 150 g Zn x 1 mol Zn / 65.4 g = 2.29 mols Zn (÷1->2.29)

for HCl we have: 73 g HCl x 1 mol HCl / 36.5 g = 2.0 mols HCl (÷2->1.0)

Since 1.0 is less than 2.29 HCl is the limiting reagent

If HCl is the limiting reagent, then Zn must be the substance that is in excess.