The reaction of butylamine (C₄H₉NH₂) with hydrochloric acid (HCl) is a simple acid-base reaction, forming butylammonium chloride (C₄H₉NH₃Cl).

Here's the balanced chemical equation:

C₄H₉NH₂ (aq) + HCl (aq) → C₄H₉NH₃Cl (aq)

Explanation:

* Butylamine (C₄H₉NH₂) is a weak base: It accepts a proton (H⁺) from the acid.

* Hydrochloric acid (HCl) is a strong acid: It readily donates a proton (H⁺).

* Butylammonium chloride (C₄H₉NH₃Cl) is a salt: It forms as the protonated butylamine cation (C₄H₉NH₃⁺) combines with the chloride anion (Cl⁻).

This reaction is an example of a neutralization reaction where an acid and a base react to form salt and water. In this case, water is not explicitly shown in the equation as it's not a major product.