Single displacement reaction
Encyclopedia
A single-displacement reaction, also called single-replacement reaction, is a type of oxidation-reduction chemical reaction
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...
This will occur if A is more reactive
than B. You can refer to the reactivity series
to be sure of this.
A and B must be either:
In either case, when AC and BC are aqueous compounds (which is usually the case), C is a spectator ion
.
In the activity or reactivity series
, the metals with the highest propensity to donate their electrons to react are listed first, and the most unreactive metals are listed last. Therefore a metal higher on the list is able to displace anything on the list below it. The order of activity for metals is Li>K>Ba>Ca>Na>Mg>Al>Mn>Zn>Cr>Fe>Co>Ni>Sn>Pb>H2>Cu>Ag>Hg>Pt>Au. Similarly, the halogens with the highest propensity to acquire electrons are the most reactive. The activity series for halogens is F>Cl>Br>I.
Due to the free state nature of A and B, all single displacement reactions are also oxidation-reduction reactions, where the key event is the movement of electrons from one reactant to another. 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 have different charge as ions and therefore some balancing of the equation may be necessary. For example the reaction between silver nitrate
, AgNO3 (Ag+), and zinc
, Zn, forms silver
, Ag, and zinc nitrate
, Zn(NO3)2 (Zn2+).
All simple metal with acid reactions are single displacement reactions. For example the reaction between magnesium
, Mg, and hydrochloric acid
, HCl, forms magnesium chloride
, MgCl2, and hydrogen
, H2.
Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)
AX + Y → YX + A
Element Y has replaced A (in a 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:
Note that if the reactant in elemental form is not the more reactive metal, then no reaction will occur. Some examples of this would be the reverse reactions to these.
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
s are here, so here are the two examples:
Again, the less reactive halogen cannot replace the more reactive halogen:
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
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 + BC → AC + B
This will occur if A is more reactive
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
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 C represents an anion; or
- halogenHalogenThe halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
s, in which case C represents a cation.
In either case, when AC and BC are aqueous compounds (which is usually the case), C 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 but does not affect the equilibrium:...
.
In the activity or 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...
, the metals with the highest propensity to donate their electrons to react are listed first, and the most unreactive metals are listed last. Therefore a metal higher on the list is able to displace anything on the list below it. The order of activity for metals is Li>K>Ba>Ca>Na>Mg>Al>Mn>Zn>Cr>Fe>Co>Ni>Sn>Pb>H2>Cu>Ag>Hg>Pt>Au. Similarly, the halogens with the highest propensity to acquire electrons are the most reactive. The activity series for halogens is F>Cl>Br>I.
Due to the free state nature of A and B, all single displacement reactions are also oxidation-reduction reactions, where the key event is the movement of electrons from one reactant to another. 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 have different charge as ions and therefore some balancing of the equation may be necessary. For example the reaction between silver nitrate
Silver nitrate
Silver nitrate is an inorganic compound with chemical formula . This compound is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides...
, AgNO3 (Ag+), and zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, Zn, forms silver
Silver
Silver is a metallic 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 highly deliquescent substance which is usually prepared by dissolving zinc in nitric acid. It can be used as a mordant in dyeing...
, Zn(NO3)2 (Zn2+).
- 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, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
, Mg, and hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
, HCl, forms magnesium chloride
Magnesium chloride
Magnesium chloride is the name for the chemical compounds with the formulas MgCl2 and its various hydrates MgCl2x. These salts are typical ionic halides, being highly soluble in water. The hydrated magnesium chloride can be extracted from brine or sea water...
, MgCl2, and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, H2.
Mg(s) + 2 HCl(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 → YX + A
Element Y has replaced A (in a 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:
- Cu + 2AgNO3 → 2Ag + Cu(NO3)2
- Fe + Cu(NO3)2 → Fe(NO3)2 + Cu
- Ca + 2H2O → Ca(OH)2 + H2
- Zn + 2HCl → ZnCl2 + H2
Note that if the reactant in elemental form is not the more reactive metal, then no reaction will occur. Some examples of this would be the reverse reactions to these.
- Ag + Cu(NO3)2 → No reaction
- Au + HCl → No reaction
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 series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
s are here, so here are the two examples:
- Cl2 + 2NaBr → 2NaCl + Br2
- Br2 + 2KI → 2KBr + I2
Again, the less reactive halogen cannot replace the more reactive halogen:
- I2 + 2KBr → no reaction