The balanced equation for the reaction of strontium (Sr) with hydrochloric acid (HCl) is:
Sr (s) + 2 HCl (aq) → SrCl2 (aq) + H2 (g)
In this reaction, solid strontium reacts with hydrochloric acid to produce aqueous strontium chloride and hydrogen gas. The coefficient ‘2’ in front of HCl ensures that there are enough chloride ions to react with one strontium atom. This demonstrates the principle of conservation of mass, meaning that the number of each type of atom on the reactant side must equal the number on the product side.