doubledisplacement

Double displacement, also called metathesis, is a type of chemical reaction in which the cations and anions of two ionic compounds exchange partners to form two new compounds. This typically occurs in aqueous solution and is driven by the formation of a product that is insoluble, neutral, or more weakly dissociated than the reactants.

During a double displacement reaction, the ionic compounds AB and CD exchange their anions and cations to yield AD and CB, with net ionic equations often used to analyze the process. In solution, spectator ions may be canceled to reveal the actual chemical change. The reaction proceeds when a driving force such as precipitation of a nearly insoluble salt, formation of a weak electrolyte like water, or release of a gas occurs.

Common examples include precipitation reactions, acid-base neutralizations, and gas-evolving reactions. Examples: NaCl + AgNO3 -> AgCl(s) + NaNO3(aq); BaCl2 + Na2SO4 -> BaSO4(s) + 2NaCl(aq). Acid-base: NaOH + HCl -> NaCl + H2O. Gas formation: Na2CO3 + 2HCl -> 2NaCl + CO2(g) + H2O.

Limitations and notes: not all combinations of ionic compounds react in this way; the reaction depends on solubility rules, acid-base affinities, and the potential to form a species that precipitates or evolves a gas. In analyses, net ionic equations help distinguish the actual chemical change by removing spectator ions.