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Single displacement reaction

 

 
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Single displacement reaction
 
 
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A single-displacement reaction, also called single-replacement reaction, is when an element or ion moves out of one compound and into another. (One element is replaced by another in a compound.) This is usually written as
A + BX ? AX + B
This will occur if A is more reactive
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
 than B. You can refer to the reactivity series
Reactivity series

In introductory chemistry, the reactivity series or activity series is an empirical series of metals, in order of "reactivity" from highest to lowest....
 to be sure of this.

A and B must be either: In either case, when AX and BX are aqueous compounds (which is usually the case), X is a spectator ion
Spectator ion

A spectator ion is an ion that exists as a reactant and a product in a chemical equation. Spectator ions can be observed in the reaction of aqueous solutions of sodium chloride and copper sulfate:...
.

Due to the free state nature of A and B, all single displacement reactions are also oxidation-reduction reactions.






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A single-displacement reaction, also called single-replacement reaction, is when an element or ion moves out of one compound and into another. (One element is replaced by another in a compound.) This is usually written as
A + BX ? AX + B
This will occur if A is more reactive
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
 than B. You can refer to the reactivity series
Reactivity series

In introductory chemistry, the reactivity series or activity series is an empirical series of metals, in order of "reactivity" from highest to lowest....
 to be sure of this.

A and B must be either:
  • different metals (hydrogen's behavior as a cation renders it as a metal here), in which case X represents an anion; or
  • halogen
    Halogen

    |}The halogens or halogen elements are a chemical series of nonmetal chemical element from Periodic table group International Union of Pure and Applied Chemistry of the periodic table, comprising fluorine, F; chlorine, Cl; bromine, Br; iodine, I; and astatine, At....
    s, in which case X represents a cation.
In either case, when AX and BX are aqueous compounds (which is usually the case), X is a spectator ion
Spectator ion

A spectator ion is an ion that exists as a reactant and a product in a chemical equation. Spectator ions can be observed in the reaction of aqueous solutions of sodium chloride and copper sulfate:...
.

Due to the free state nature of A and B, all single displacement reactions are also oxidation-reduction reactions. When A and B are metals, A is always oxidized and B is always reduced. Since halogens prefer to gain electrons, A is reduced (from a 0 to -1) and B is oxidized (from -1 to 0) when A and B represent those elements.

A and B may not have the same charge when ions are formed therefore some balancing of the equation may be necessary. For example the reaction between silver nitrate
Silver nitrate

Silver nitrate, also known as lunar caustic, is a soluble chemical compound with chemical formula silverNitrogenOxygen3. This compound is a versatile precursor to many other silver compounds, such as those used in photography....
, AgNO3, and zinc
Zinc

Zinc is a metallic chemical element with the symbol Zn and atomic number 30. It is a first-row transition metal of the group 12 element of the periodic table....
, Zn, forms silver
Silver

Silver is a chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal....
, Ag, and zinc nitrate
Zinc nitrate

Zinc nitrate is a chemical compound used as a mordant in dyeing. It is also a source of zinc ions for chemistry. An example reaction gives a precipitate of zinc carbonate: Zn2 + Sodium carbonate ? ZnCO3 + 2 Sodium nitrate....
, Zn(NO3)2.

2AgNO3(aq) + Zn(s) ? 2Ag(s) + Zn(NO3)2(aq)


All simple metal with acid reactions are single displacement reactions. For example the reaction between magnesium
Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....
, Mg, and hydrochloric acid
Hydrochloric acid

Hydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong acid mineral acid and has major industrial uses....
, HCl, forms magnesium chloride
Magnesium chloride

Magnesium chloride is the name for the chemical compounds with the chemical formulas MgCl2 and its various water of hydrations MgCl2x....
, MgCl2, and hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
, H2.

Mg(s) + 2HCl(aq) ? MgCl2(aq) + H2(g)


Cation replacement

One cation replaces another. A cation is a positively charged ion or a metal. When it is written in generic symbols, it is written out like this:

AX + Y ? YXh

Element Y has replaced A (in the compound AX) to become a new compound YX and the free element A. This is an oxidation-reduction reaction wherein element A is reduced from a cation into the elemental form and element Y is oxidized from the elemental form into a cation. Some examples are:
  1. Cu + 2AgNO3 ? 2Ag + Cu(NO3)2
  2. Fe + Cu(NO3)2 ? Fe(NO3)2 + Cu
  3. Ca + 2H2O ? Ca(OH)2 + H2
  4. Zn + 2HCl ? ZnCl2 + H2


Anion replacement

One anion replaces another. An anion is a negatively charged ion or a nonmetal. Written using generic symbols, it is:

A + XY ? XA + Y

Element A has replaced Y (in the compound XY) to form a new compound XA and the free element Y. This is an oxidation-reduction reaction wherein element A is reduced from the elemental form into an anion and element Y is oxidized from an anion into the elemental form.

Some of the only examples that involve halogen
Halogen

|}The halogens or halogen elements are a chemical series of nonmetal chemical element from Periodic table group International Union of Pure and Applied Chemistry of the periodic table, comprising fluorine, F; chlorine, Cl; bromine, Br; iodine, I; and astatine, At....
s are here, so here are the two examples:
  1. Cl2 + 2NaBr ? 2NaCl + Br2
  2. Br2 + 2KI ? 2KBr + I2


See also

  • Double displacement reaction