Displacement Reactions

The number of reactants and products does not change during a displacement reaction. Instead, an atom or ion in a compound is displaced by an atom or ion of one or more of the other substances in the reaction.  Displacement reactions are often classified further as single displacement and double displacement reactions.  This page will summarize the main concept necessary to identify double and single displacement reaction.  In the page that follows, acid-base and oxidation-reduction reactions, two important kinds of displacement reactions will be discussed in detail.

Single Displacement Reactions:  
 

General Form	Important Points
X + YZ  XZ + Y	The most reactive metals displace hydrogen from water or acids More reactive metals can displace less reactive metal ions from solution A halogen displaces another halide ion from solution (F displaces all other halogens, Cl displaces Br and I, and Br displaces I following top to bottom order in periodic table) To determine the order of metal reactivity consult a Metal Activity Series.
Examples	2Al(s) + 6H2O(g)  2Al(OH)3(s) + 3H2(g) Ni(s) + 2HCl(aq)  NiCl2(aq) + H2(g) Cu(NO3)2(aq) + Zn(s)   Cu(s) + Zn(NO3)2(aq) 2KBr(aq) + Cl2(g)  Br2(aq) + 2KCl(aq)

Double Displacement Reactions:  
 

General Form	Important Points
WX + YZ  WZ + XY	There are 3 common aqueous phase double displasement reactions: precipitation reactions, neutralization reactions and reactions where a gas is produced. In order to determine if a solid precipitate will be produced, you must consult the solubility rules. If all products are soluble then no change or reaction has occurred in the solution. A neutralization reaction involves an acid and a base and the products always include a salt and water. Carbonate or sulfites react with acids to form a gas.
Examples	AgNO3(aq) + KBr(aq)  AgBr(s) + KNO3 ( AgBr was found to be insoluble by checking the solubility rules) 3HCl(aq) + Al(OH)3(s)  AlCl3(aq) + H2O(l) (Acid-base neutralization) MgCO3(s) + 2HCl(aq)   MgCl2(aq)  + H2O(l)  + CO2(g) (Gas produced)