the balanced equation for the above reaction is as follows; Mg + 2HCl ---> MgCl₂ + H₂ stoichiometry of Mg to HCl is 1:2 number of Mg moles reacted - 3.5 mol 1 mol of Mg reacts with 2 mol of HCl therefore 3.5 mol of Mg requires - 2 x 3.5 = 7.0 mol of HCl number of HCl moles required to completely react with 3.5 mol of Mg is 7.0 mol of HCl