When magnesium (Mg) reacts with hydrochloric acid (HCl), the products of the reaction are magnesium chloride (MgCl2) and hydrogen gas (H2). The chemical equation for this reaction is:

Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)

In this reaction, magnesium loses its valence electrons to the chloride ions (Cl-) in hydrochloric acid, forming magnesium chloride. The hydrogen ions (H+) from hydrochloric acid combine with electrons from magnesium, forming hydrogen gas. The resulting solution contains magnesium chloride dissolved in water and hydrogen gas released as a product of the reaction.