 In the single displacement reaction of a metal with an acid, we will react magnesium metal with hydrochloric acid. As we add the magnesium metal, we get a very rapid reaction. Hydrogen gas is produced by the single displacement reaction. The metal reacts completely, leaving us the solution of magnesium chloride. We can test for the presence of the hydrogen gas by bringing in a burning splint. The hydrogen gas is flammable and ignites.