Consider the reaction between HCl and O2: 4HCl grams + O2 - 2 H2O liquid + 2 Cl2 grams When 63.1 grams of HCl react with 17.2 g of O2, 49.3 grams of Cl2 are collected. What is the limiting reactant?

The balanced equation for the above reaction is as follows;

4HCl + O₂ - - - > 2H₂O + 2Cl₂

stoichiometry of HCl to O₂ is 4:1

number of HCl moles present - 63.1 g / 36.5 g/mol = 1.73 mol

number of O₂ moles present - 17.2 g / 32 g/mol = 0.54 mol

if HCl is the limiting reactant; then number of O₂ moles = 1.73/4 = 0.43 mol

There are 0.54 mol present and only 0.43 mol are required to react. Therefore HCl is the limiting reactant and O₂ is in excess.