Single displacement reaction
chemical reaction concerning the exchange of ions
A single-displacement reaction, also known as single replacement reaction or exchange reaction, is a type of chemical reaction in which one element or ligand is replaced by an atom or group.
It can be represented generically as:
A
+
BC
⟶
AC
+
B
{\displaystyle {\ce {A + BC -> AC + B}}}
where either
A
{\displaystyle {\ce {A}}}
and
B
{\displaystyle {\ce {B}}}
are different metals (or any element that forms cation like hydrogen) and
C
{\displaystyle {\ce {C}}}
is an anion; or
A
{\displaystyle {\ce {A}}}
and
B
{\displaystyle {\ce {B}}}
are halogens and
C
{\displaystyle {\ce {C}}}
is a cation.
This will most often occur if
A
{\displaystyle {\ce {A}}}
is more reactive than
B
{\displaystyle {\ce {B}}}
, thus giving a more stable product. The reaction in that case is exergonic and spontaneous.
In the first case, when
A
{\displaystyle {\ce {A}}}
and
B
{\displaystyle {\ce {B}}}
are metals,
BC
{\displaystyle {\ce {BC}}}
and
AC
{\displaystyle {\ce {AC}}}
are usually aqueous compounds (or very rarely in a molten state) and
C
{\displaystyle {\ce {C}}}
is a spectator ion (i.e. remains unchanged).
A
(
s
)
+
B
+
(
aq
)
+
C
−
(
aq
)
⏟
BC
(
aq
)
⟶
A
+
(
aq
)
+
C
−
(
aq
)
⏟
AC
(
aq
)
+
B
(
s
)
{\displaystyle {\ce {A(s) + \underbrace{B+(aq) + C^{-}(aq)}_{BC(aq)}-> \underbrace{A+(aq) + C^{-}(aq)}_{AC(aq)}+ B(s)}}}
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:
K
>
Na
>
Ca
>
Mg
>
Al
>
C
>
Zn
>
Fe
>
NH
4
+
>
H
+
>
Cu
>
Ag
>
Au
{\displaystyle {\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}}}
(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:
F
2
>
Cl
2
>
Br
2
>
I
2
{\displaystyle {\ce {F2>Cl2>Br2>I2}}}
Due to the free state nature of
A
{\displaystyle {\ce {A}}}
and
B
{\displaystyle {\ce {B}}}
, single displacement reactions are also redox reactions, involving the transfer of electrons from one reactant to another.
Begin with the source’s own compact description: “Single displacement reaction” is chemical reaction concerning the exchange of ions. The dossier treats that line as a proposition to test through Single, displacement and reaction, not as a finished interpretation.
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