Chemistry:Single displacement reaction

Short description: Type of chemical reaction

A single-displacement reaction, also known as single replacement reaction or exchange reaction, is a chemical reaction in which one element is replaced by another in a compound.^[1]^[2]^[3]

It can be represented generically as:

A + B C ⟶ A C + B

where either

$A$ and $B$ are different metals (or any element that forms cation like hydrogen) and $C$ is an anion;^[2] or

$A$ and $B$ are halogens and $C$ is a cation.^[2]

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, $B C$ and $A C$ are usually aqueous compounds (or very rarely in a molten state) and $C$ is a spectator ion (i.e. remains unchanged).^[1]

A (s) + \underset{B C (a q)}{\underset{⏟}{B^{+} (a q) + C^{-} (a q)}} ⟶ \underset{A C (a q)}{\underset{⏟}{A^{+} (a q) + C^{-} (a q)}} + B (s)

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:^[1]

K > C a > N a > M g > A l > C > Z n > F e > N H_{4}^{+} > H^{+} > C u > A g > A u

(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: ^[1]^[2]^[3]

F_{2} > C l_{2} > B r_{2} > I_{2}

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.^[4] 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 + B C ⟶ A C + B

(Element A has replaced B in compound BC to become a new compound AC and the free element B.)

Some examples are:

F e + C u S O_{4} ⟶ F e S O_{4} + C u (v)

(Blue vitriol)____(Green vitriol)

Z n + C u S O_{4} ⟶ Z n S O_{4} + C u (v)

(Blue vitriol)___(White vitriol)

Z n + F e S O_{4} ⟶ Z n S O_{4} + F e (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.^[5]

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.

F e + Z n S O_{4} ⟶

No Reaction

Anion replacement

Here one anion replaces another:

A + C B ⟶ C A + B

(Element A has replaced B in the compound CB to form a new compound CA and the free element B.)

Some examples are: $C l_{2} + 2 N a B r ⟶ 2 N a C l + B r_{2} (v)$ $B r_{2} + 2 K I ⟶ 2 K B r + I_{2} (v)$ $C l_{2} + H_{2} S ⟶ 2 H C l + S (v)$

Again, the less reactive halogen cannot replace the more reactive halogen:

I_{2} + 2 K B r ⟶

no reaction

Common reactions

Metal-acid reaction

Metals react with acids to form salts and hydrogen gas.

Z n (s) + 2 H C l (a q) ⟶ Z n C l_{2} (a q) + H_{2} ↑

^[2]^[3]

However less reactive metals can not displace the hydrogen from acids.^[3] (They may react with oxidizing acids though.)

C u + H C l ⟶

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.

F e (s) + H_{2} O (g) ⟶ F e O (s) + H_{2} ↑

C a (s) + 2 H_{2} O (l) ⟶ C a (O H)_{2} (a q) + H_{2} ↑

The reaction can be extremely violent with alkali metals as the hydrogen gas catches fire.^[2]

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,^[6] such as in the carbothermic reaction of zinc oxide (zincite) to produce zinc metal:

Z n O + C ⟶ Z n + C O

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

3 M n O_{2} + 4 A l ⟶ 3 M n + 2 A l_{2} O_{3}

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

3 S i O_{2} + 4 A l ⟶ 3 S i + 2 A l_{2} O_{3}

B_{2} O_{3} + 3 M g ⟶ 2 B + 3 M g O

T i C l_{4} + 2 M g ⟶ T i + 2 M g C l_{2}

W F_{6} + 3 H_{2} ⟶ W + 6 H F

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.^[6]

F e_{2} O_{3} (s) + 2 A l (s) ⟶ 2 F e (l) + A l_{2} O_{3} (s)

a(Haematite)

3 C u O + 2 A l ⟶ 3 C u + A l_{2} O_{3}

Silver tarnish

Silver tarnishes due to the presence of hydrogen sulfide, leading to formation of silver sulfide.^[7]^[2]

4 A g + 2 H_{2} S + O_{2} ⟶ 2 A g_{2} S + 2 H_{2} O

3 A g_{2} S + 2 A l ⟶ 6 A g + A l_{2} S_{3}

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 $C u C l_{2}$ .

4 H C l + O_{2} ⟶ 2 C l_{2} + 2 H_{2} O

Bromine and iodine are extracted form brine by displacing with chlorine.

2 H B r + C l_{2} ⟶ 2 H C l + B r_{2} ↑

2 H I + C l_{2} ⟶ 2 H C l + I_{2} ↑

References

↑ ^1.0 ^1.1 ^1.2 ^1.3 "Single replacement reactions" (in en). https://www.khanacademy.org/science/ap-chemistry/chemical-reactions-ap/types-of-chemical-reactions-ap/a/single-replacement-reactions.
↑ ^2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 ^2.6 "Single Replacement Reactions" (in en). 2016-06-27. https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory_Chemistry_(CK-12)/11%3A_Chemical_Reactions/11.07%3A_Single_Replacement_Reactions.
↑ ^3.0 ^3.1 ^3.2 ^3.3 "Types of Chemical Reactions: Single- and Double-Displacement Reactions". https://courses.lumenlearning.com/suny-introductory-chemistry/chapter/types-of-chemical-reactions-single-and-double-displacement-reactions/.
↑ Silberberg. Chemistry, the Molecular Nature of Matter and Change, 4th ed. p. 150 McGraw Hill 2006.
↑ "Exothermic metal displacement reactions" (in en). https://edu.rsc.org/experiments/exothermic-metal-displacement-reactions/1730.article.
↑ ^6.0 ^6.1 "Displacement reactions of metal oxides" (in en-GB). https://www.bbc.co.uk/bitesize/guides/z6c26yc/revision/1.
↑ JCE staff (2000-03-01). "Silver to Black - and Back". Journal of Chemical Education 77 (3): 328A. doi:10.1021/ed077p328A. ISSN 0021-9584. Bibcode: 2000JChEd..77R.328J. https://pubs.acs.org/doi/abs/10.1021/ed077p328A.

External links

Reactivity series by RSC

Halogen displacement reaction by RSC

Chlorine water reacting with Iodide and Bromide, YouTube

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Original source: https://en.wikipedia.org/wiki/Single displacement reaction. Read more

[:1-1] 1.0 ^1.1 ^1.2 ^1.3 "Single replacement reactions" (in en). https://www.khanacademy.org/science/ap-chemistry/chemical-reactions-ap/types-of-chemical-reactions-ap/a/single-replacement-reactions.

[:2-2] 2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 ^2.6 "Single Replacement Reactions" (in en). 2016-06-27. https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory_Chemistry_(CK-12)/11%3A_Chemical_Reactions/11.07%3A_Single_Replacement_Reactions.

[:3-3] 3.0 ^3.1 ^3.2 ^3.3 "Types of Chemical Reactions: Single- and Double-Displacement Reactions". https://courses.lumenlearning.com/suny-introductory-chemistry/chapter/types-of-chemical-reactions-single-and-double-displacement-reactions/.

[4] Silberberg. Chemistry, the Molecular Nature of Matter and Change, 4th ed. p. 150 McGraw Hill 2006.

[5] "Exothermic metal displacement reactions" (in en). https://edu.rsc.org/experiments/exothermic-metal-displacement-reactions/1730.article.

[:4-6] 6.0 ^6.1 "Displacement reactions of metal oxides" (in en-GB). https://www.bbc.co.uk/bitesize/guides/z6c26yc/revision/1.

[:0-7] JCE staff (2000-03-01). "Silver to Black - and Back". Journal of Chemical Education 77 (3): 328A. doi:10.1021/ed077p328A. ISSN 0021-9584. Bibcode: 2000JChEd..77R.328J. https://pubs.acs.org/doi/abs/10.1021/ed077p328A.

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Cation replacement

Anion replacement