Write a balanced chemical equation for the reaction of magnesium with hydrochloric acid (HCI (aq) to form Magnesium chloride and hydrogen gas:

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

Looking at the equation:

We have 1 Mg at the left hand side and 1 Mg as well on the right hand side.

So that is balanced.

We have 1 H at the left hand side and 2 H on the right hand side.

So that is not balanced. Same for Chlorine. Cl.

We add 2 to the HCl on the left hand side and that balances it.

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

The equation is

Mg + 2HCl - > MgCl2 + H2