A double replacement reaction is a type of chemical reaction where two compounds exchange components to form two new compounds. This typically occurs in aqueous solutions, where the reactants are dissolved in water. The general form of this reaction can be represented as AB + CD → AD + CB, where A and C are cations, and B and D are anions. These reactions often involve the formation of a precipitate, gas, or water, which drives the reaction forward. Common examples include the reaction between sodium chloride and silver nitrate, resulting in the formation of silver chloride precipitate and sodium nitrate. Double replacement reactions are essential in various applications, including titration and water treatment.