Ammonium salt A product of a reaction between ammonia, NH3, and various acids. The general reaction for formation is NH3 + HX –+ NH2X. Examples of ammonium salts are ammonium chloride, NH4Cl, ammonium nitrate, NH4NO3, These compounds are addition products of ammonia and the acid. For this reason, their formulas are sometimes written as [H(NH3)]X.