The reaction between magnesium Mg and hydrochloric acid HCl can be represented by the following balanced chemical equation:Mg + 2HCl MgCl2 + H2To determine the mass of the product magnesium chloride, MgCl2 formed, we will use stoichiometry. First, we need to find the molar mass of magnesium and magnesium chloride:Molar mass of Mg = 24.31 g/molMolar mass of MgCl2 = 24.31 g/mol Mg + 2 * 35.45 g/mol Cl = 95.21 g/molNow, we will convert the given mass of magnesium 15.0 grams to moles:moles of Mg = mass of Mg / molar mass of Mgmoles of Mg = 15.0 g / 24.31 g/mol = 0.617 molesAccording to the balanced chemical equation, 1 mole of Mg reacts with 2 moles of HCl to produce 1 mole of MgCl2. Therefore, the moles of MgCl2 produced will be equal to the moles of Mg reacted:moles of MgCl2 = 0.617 molesNow, we will convert the moles of MgCl2 to mass:mass of MgCl2 = moles of MgCl2 * molar mass of MgCl2mass of MgCl2 = 0.617 moles * 95.21 g/mol = 58.75 gSo, the mass of magnesium chloride MgCl2 formed when 15.0 grams of magnesium reacts with excess hydrochloric acid is approximately 58.75 grams.