To calculate the percent yield of the reaction, we first need to determine the limiting reactant and the actual yield of magnesium chloride.1. Determine the moles of reactants:Moles of magnesium Mg = mass / molar massMg has a molar mass of 24.31 g/mol.Moles of Mg = 12.5 g / 24.31 g/mol = 0.514 molMoles of hydrochloric acid HCl = mass / molar massHCl has a molar mass of 36.46 g/mol.Moles of HCl = 15.0 g / 36.46 g/mol = 0.411 mol2. Determine the limiting reactant:The balanced chemical equation for the reaction is:Mg + 2HCl MgCl2 + H2From the balanced equation, we can see that 1 mol of Mg reacts with 2 mol of HCl. Therefore, we need to compare the mole ratio of Mg to HCl to determine the limiting reactant.Mole ratio of Mg to HCl = 0.514 mol Mg / 0.411 mol HCl = 1.25Since the mole ratio is greater than 1, HCl is the limiting reactant.3. Calculate the actual yield of magnesium chloride MgCl2 :Using the stoichiometry from the balanced equation, 2 mol of HCl produces 1 mol of MgCl2. Therefore, we can calculate the moles of MgCl2 produced:Moles of MgCl2 = 0.411 mol HCl * 1 mol MgCl2 / 2 mol HCl = 0.2055 mol MgCl2Now, convert the moles of MgCl2 to grams:Mass of MgCl2 = moles * molar massMgCl2 has a molar mass of 95.21 g/mol.Mass of MgCl2 = 0.2055 mol * 95.21 g/mol = 19.56 g4. Calculate the percent yield:Percent yield = actual yield / theoretical yield * 100Percent yield = 19.56 g / 25.7 g * 100 = 76.1%The percent yield of the reaction is 76.1%.