The balanced reaction that describes the reaction between hydrogen and chlorine to produce hydrogen chloride is expressed H2 + Cl2 = 2HCl. Hence for every mole hydrogen chloride produced, there is 1 mole of hydrogen and chlorine needed. When 1 mole each of the reactants are used, there is 72.9 grams of HCl produced. We multiply 2 with the molar mass of HCl.
