Iron dissolves in hydrochloric acid because of a chemical reaction between the two substances. Here's the chemical equation for the reaction:

```

Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g)

```

In this reaction, solid iron (Fe) reacts with hydrochloric acid (HCl) to form iron(II) chloride (FeCl2) and hydrogen gas (H2). The reaction occurs because iron is more reactive than hydrogen, so it is able to replace the hydrogen atoms in HCl.

The reaction between iron and hydrochloric acid is exothermic, which means that it releases heat. This heat can be used to dissolve the iron, which is why it is often used in industrial processes.