If an active metal reacts with certain acids such as hydrochloric acid, it yields a salt and hydrogen gas. The general reaction is:

$$Metal \space (s) + Hydrochloric \space acid \space (aq) \longrightarrow Salt \space (aq)+Hydrogen \space gas \space (g)$$

For example, when iron reacts with hydrochloric acid, it produces iron(II) chloride and hydrogen gas:

$$Fe \space (s) + 2HCl \space (aq) \longrightarrow FeCl2 \space (aq)+H2 \space (g)$$

Similarly, when zinc reacts with hydrochloric acid, it produces zinc chloride and hydrogen gas:

$$Zn \space (s) + 2HCl \space (aq) \longrightarrow ZnCl2 \space (aq)+H2 \space (g)$$

The reactivity of active metals with acids varies depending on the metal. Some metals, such as potassium and sodium, react very vigorously with acids, while others, such as copper and silver, react more slowly.