Single displacement reaction

A single-displacement reaction, also known as single replacement reaction or exchange reaction, is an archaic concept in chemistry. It describes the stoichiometry of some chemical reactions in which one element or ligand is replaced by an atom or group.{{Cite web|last=|first=|date=|title=Single replacement reactions|url=https://www.khanacademy.org/science/ap-chemistry/chemical-reactions-ap/types-of-chemical-reactions-ap/a/single-replacement-reactions|archive-url=|archive-date=|access-date=|website=Khan Academy|language=en}}{{Cite web|last=|first=|date=2016-06-27|title=Single Replacement Reactions|url=https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory_Chemistry_(CK-12)/11%3A_Chemical_Reactions/11.07%3A_Single_Replacement_Reactions|archive-url=|archive-date=|access-date=|website=Chemistry LibreTexts|language=en}}{{Cite web|last=|first=|date=|title=Types of Chemical Reactions: Single- and Double-Displacement Reactions|url=https://courses.lumenlearning.com/suny-introductory-chemistry/chapter/types-of-chemical-reactions-single-and-double-displacement-reactions/|archive-url=|archive-date=|access-date=|website=courses.lumenlearning.com}}

It can be represented generically as:

:A + BC -> AC + B

where either

A and B are different metals (or any element that forms cation like hydrogen) and C is an anion; or

A and B are halogens and C is a cation.

This will most often occur if A is more reactive than B, thus giving a more stable product. The reaction in that case is exergonic 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{B+(aq) + C^{-}(aq)}_{BC(aq)} -> \underbrace{A+(aq) + C^{-}(aq)}_{AC(aq)} + B(s)

File: Precipitation of Silver on Copper 2.jpg

File:Single Displacement AgNO3 and Cu.ogv

File:Zinc displaces Tin.webm

In the reactivity series, 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:

: $\ce{K} > \ce{Na} > \ce{Ca} > \ce{Mg} > \ce{Al} > {\color{gray}\ce{C}} > \ce{Zn} > \ce{Fe} > {\color{gray}\ce{NH4^+}} > {\color{gray}\ce{H+}} > \ce{Cu} > \ce{Ag} > \ce{Au}$

: {{small|(Hydrogen, carbon and ammonium — labeled in gray — are not metals.)}}

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 reactions, involving the transfer of electrons from one reactant to another.Silberberg. Chemistry, the Molecular Nature of Matter and Change, 4th ed. p. 150 McGraw Hill 2006. 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 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 -> FeSO4 + Cu

:::(Blue vitriol){{font color|white|____}}(Green vitriol)

:Zn + CuSO4 -> ZnSO4 + Cu

:::(Blue vitriol){{font color|white|___}}(White vitriol)

:Zn + FeSO4 -> ZnSO4 + Fe

:::(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.{{Cite web|others=Nuffield Foundation|title=Exothermic metal displacement reactions|url=https://edu.rsc.org/experiments/exothermic-metal-displacement-reactions/1730.article|access-date=|website=RSC Education|language=en}}

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

{{External media|video1=[https://www.youtube.com/watch?v=yWcSzvJ6Kcw CuCl₂ and Iron Part 2], 2011|video2=[https://www.youtube.com/watch?v=gqSXWbS6gzo Reaction of CuCl₂ with Al], 2011|video3=[https://www.youtube.com/watch?v=gqGrpd5smtI Copper Sulfate and Iron: Part 1], 2011}}

Anion replacement

Here one anion 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

Br2 + 2KI -> 2KBr + I2(v)

Cl2 + H2S -> 2HCl + S(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.

File:Zn reaction with HCl.JPG

:Zn(s) + 2HCl(aq) -> ZnCl2(aq) + H2 ^

However, less reactive metals cannot 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) -> FeO(s) + H2 ^

:Ca(s) + 2H2O (l) -> Ca(OH)2(aq) + H2 ^

File: Sodium and Water.png

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.

{{External media|video1=[https://www.youtube.com/watch?v=oqMN3y8k9So Reaction of Potassium and Water], 2011|caption=|video2=[https://www.youtube.com/watch?v=u_1uLP30uxY Reaction of Magnesium and Water], 2011}}

=Metal extraction=

Coke or more reactive metals are used to reduce metals by carbon from their metal oxides, such as in the carbothermic reaction of zinc oxide (zincite) to produce zinc metal:

:ZnO + C -> Zn + CO

and the use of aluminium to produce manganese from manganese dioxide:

:3MnO2 + 4Al -> 3Mn + 2Al2O3

Such reactions are also used in extraction of boron, silicon, titanium and tungsten.

:3SiO2 + 4Al -> 3Si + 2Al2O3

:B2O3 + 3Mg -> 2B + 3MgO

:TiCl4 + 2Mg -> Ti + 2MgCl2

:WF6 + 3 H2 -> W + 6 HF

=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.{{Cite web|title=Displacement reactions of metal oxides|url=https://www.bbc.co.uk/bitesize/guides/z6c26yc/revision/1|access-date=|website=BBC Bitesize|language=en-GB}}

File:Thermite welding 03.jpg reaction proceeding for a railway welding: Shortly after this, the liquid iron flows into the mould around the rail gap]]

:Fe2O3(s) + 2 Al(s) -> 2 Fe(l) + Al2O3(s)

{{font color|white|a}}(Haematite)

:3CuO + 2Al -> 3Cu + Al2O3

=Silver tarnish=

File:1804 dollar type I reverse.jpeg

Silver tarnishes due to the presence of hydrogen sulfide, leading to formation of silver sulfide.{{Cite journal|last=JCE staff|date=2000-03-01|title=Silver to Black - and Back|url=https://pubs.acs.org/doi/abs/10.1021/ed077p328A|journal=Journal of Chemical Education|volume=77|issue=3|pages=328A|doi=10.1021/ed077p328A|bibcode=2000JChEd..77R.328J |issn=0021-9584}}

:4Ag + 2H2S + O2 -> 2Ag2S + 2H2O

: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 from brine by displacing with chlorine.

:2HBr + Cl2 -> 2HCl + Br2 ^

:2HI + Cl2 -> 2HCl + I2 ^

References

External links

[https://www.youtube.com/watch?v=fJ6cDG6Fbeo Reactivity series] by RSC

[https://www.youtube.com/watch?v=TMwpLNZJmQo Halogen displacement reaction] by RSC

[https://m.youtube.com/watch?v=I2t_Sg3A7MQ Chlorine water reacting with Iodide and Bromide], YouTube

Category:Chemical reactions