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A single-displacement reaction, also known as single replacement reaction or exchange reaction, is a
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breakin ...
in which one element is replaced by another in a compound. It can be represented generically as: :A + BC -> AC + B where either *A and B are different
metals A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typical ...
(or any element that forms
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
like hydrogen) and C is an
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
; or *A and B are
halogen The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this grou ...
s and C is a
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
. This will most often occur if A is more
reactive Reactive may refer to: *Generally, capable of having a reaction (disambiguation) *An adjective abbreviation denoting a bowling ball coverstock made of reactive resin * Reactivity (chemistry) *Reactive mind *Reactive programming See also *Reactan ...
than B, thus giving a more stable product. The reaction in that case is
exergonic An exergonic process is one which there is a positive flow of energy from the system to the surroundings. This is in contrast with an endergonic process. Constant pressure, constant temperature reactions are exergonic if and only if the Gibbs f ...
and spontaneous. In the first case, when A and B are metals, BC and AC are usually aqueous compounds (or very rarely in a molten state) and C is a spectator ion (i.e. remains unchanged). : A(s) + \underbrace_ -> \underbrace_ + B(s) In the
reactivity series In chemistry, a reactivity series (or activity series) is an empirical, calculated, and structurally analytical progression of a series of metals, arranged by their "reactivity" from highest to lowest. It is used to summarize information about th ...
, the metals with the highest propensity to donate their electrons to react are listed first, followed by less reactive ones. Therefore, a metal higher on the list can displace anything below it. Here, is a condensed version of the same: : \ce > \ce > \ce > \ce > \ce > > \ce > \ce > > > \ce > \ce > \ce : Similarly, the halogens with the highest propensity to acquire electrons are the most reactive. The activity series for halogens is: : F2>Cl2>Br2>I2 Due to the free state nature of A and B, single displacement reactions are also
redox Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
reactions, involving the transfer 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 0 to -1) and B is oxidized (from -1 to 0).


Cation replacement

Here one
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
replaces another: : A + BC -> AC + B (Element A has replaced B in compound BC to become a new compound AC and the free element B.) Some examples are: :Fe + CuSO4 -> Fe(SO4) + Cu(v) :::(Blue vitriol)(Green vitriol) :Zn + CuSO4 -> ZnSO4 + Cu(v) :::(Blue vitriol)(White vitriol) :Zn + FeSO4 -> ZnSO4 + Fe(v) :::(Green vitriol) (White vitriol) These reactions are exothermic and the rise in temperature is usually in the order of the reactivity of the different metals. 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. :Fe + ZnSO4 -> No Reaction : : :


Anion replacement

Here one
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
replaces another: : A + CB -> CA + B (Element A has replaced B in the compound CB to form a new compound CA and the free element B.) Some examples are: Cl2 + 2NaBr -> 2NaCl + Br2(v) Br2 + 2KI -> 2KBr + I2(v) Again, the less reactive halogen cannot replace the more reactive halogen: :I2 + 2KBr -> no reaction


Common reactions


Metal-acid reaction

Metals react with acids to form salts and hydrogen gas. :Zn(s) + 2HCl(aq) -> ZnCl2(aq) + H2 ^ However less reactive metals can not displace the hydrogen from acids. (They may react with oxidizing acids though.) :Cu + HCl -> No reaction


Reaction between metal and water

Metals react with water to form metal oxides and hydrogen gas. The metal oxides further dissolve in water to form alkalies. :Fe(s) + H2O (g) -> Fe2O3(s) + H2 ^ :Ca(s) + H2O (l) -> CaOH(aq) + H2 ^ The reaction can be extremely violent with alkali metals as the hydrogen gas catches fire. Metals like gold and silver, which are below hydrogen in the reactivity series, do not react with water.


Metal extraction

Coke or more reactive metals are used to reduce metals by carbon from their metal oxides, such as in the
carbothermic reaction Carbothermic reactions involve the reduction of substances, often metal oxides (O^2-), using carbon as the reducing agent. These chemical reactions are usually conducted at temperatures of several hundred degrees Celsius. Such processes are applie ...
of
zinc oxide Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cemen ...
(zincite) to produce
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic t ...
metal: :ZnO + C -> Zn + CO and the use of
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ...
to produce
manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial all ...
from
manganese dioxide Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for is for dry-cel ...
: :3MnO2 + 4Al -> 3Mn + 2Al2O3 Even for reactions that run in the direction opposite of their intrinsic reactivities, displacement can be driven to occur, as in the Acheson process for displacing
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...
from
silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
using
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes u ...
: :SiO2 + 2C -> Si + 2CO


Thermite reaction

Using highly reactive metals as reducing agents leads to exothermic reactions that melt the metal produced. This is used for welding railway tracks. :Fe2O3(s) + 2 Al(s) -> 2 Fe(l) + Al2O3(s) (Haematite) :3CuO + 2Al -> 3Cu + Al2O3


Silver tarnish

Silver
tarnish Tarnish is a thin layer of corrosion that forms over copper, brass, aluminum, magnesium, neodymium and other similar metals as their outermost layer undergoes a chemical reaction. Tarnish does not always result from the sole effects of oxygen ...
es due to the presence of
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
, leading to formation of
silver sulfide Silver sulfide is an inorganic compound with the formula . A dense black solid, it is the only sulfide of silver. It is useful as a photosensitizer in photography. It constitutes the tarnish that forms over time on silverware and other silver ob ...
. :2Ag + H2S -> Ag2S + H2 Its removal also involves a displacement reaction. :3Ag2S + 2Al -> 6Ag + Al2S3


Extraction of halogens

Chlorine is manufactured industrially by the Deacon's process. The reaction takes place at about 400 to 450 °C in the presence of a variety of catalysts such as CuCl2. :4HCl + O2 -> 2 Cl2 + 2H2O Bromine and iodine are extracted form brine by displacing with chlorine. :2HBr + Cl2 -> 2HCl + Br2 ^ :2HI + Cl2 -> 2HCl + I2 ^


See also

* Double-displacement reaction * Decomposition reaction * Combination reaction *
Substitution reaction A substitution reaction (also known as single displacement reaction or single substitution reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions ...
*


References

{{Reflist


External links


Reactivity series
by RSC
Halogen displacement reaction
by RSC
Chlorine water reacting with Iodide and Bromide
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Chemical reactions