When active metals react with dilute acids, they typically produce a salt and hydrogen gas. The hydrogen gas is observed as bubbles and can be identified by a 'pop' sound when a burning splinter is brought near it. For example, when zinc metal reacts with dilute hydrochloric acid, it forms zinc chloride and releases hydrogen gas. The chemical equation is: $Zn + 2HCl \rightarrow ZnCl_2 + H_2$. This demonstrates the displacement of hydrogen from the acid by the more reactive metal.