The balanced equation for the reaction of rust, Fe2O3, and hydrochloric acid, HCl is:
Fe2O3 + 6HCl → 2FeCl3 + 3H2O
In this reaction, the hydrochloric acid reacts with the rust (iron oxide) to form iron(III) chloride and water.
The balanced equation shows that 1 mole of Fe2O3 reacts with 6 moles of HCl to produce 2 moles of FeCl3 and 3 moles of H2O.