Reactivity series

In chemistry, the reactivity series is a series of metals, in order of reactivity from highest to lowest. It is used to determine the products of single displacement reactions, whereby metal A will replace another metal B in a solution if A is higher in the series.

Differing definitions

In the UK a reduced version of the below series is taught as part of the GCSE chemistry course, leading to various mnemonics being invented to aid memory. The reactivity series taught in the US is defined by the ease of oxidation and corresponds to the ordering of the table of standard electrode potentials. This is markedly different from the table below.

A reactivity series of common metals

Here is a series of some of the most common metals, listed in descending order of reactivity.

Metals	Metal Ion	Reactivity
K	K+	reacts with water
Na	Na+
Ca	Ca2+
Li	Li+
Ba	Ba2+
Sr	Sr2+
Mg	Mg2+	reacts with acids
Al	Al3+
Mn	Mn2+
Zn	Zn2+
Cr	Cr2+
Fe	Fe2+
Cd	Cd2+
Co	Co2+
Ni	Ni2+
Sn	Sn2+
Pb	Pb2+
H2	H+	included for comparison
Sb	Sb3+	highly unreactive
Bi	Bi3+
Cu	Cu2+
Hg	Hg2+
Ag	Ag+
Au	Au3+
Pt	Pt+

A metal can replace metals listed below it in the activity series, but not above. For example, sodium is highly active and thus able to replace hydrogen from water:

2 Na (s) + 2 H₂O (l) → 2 NaOH (aq) + H₂ (g)

Metals that can replace hydrogen within acids but not water are listed in the middle of the activity series, for example zinc replaces hydrogen in sulfuric acid:

Zn (s) + H₂SO₄ (aq) → ZnSO₄ (aq) + H₂ (g)

The reactivity series has applications in electrochemistry, where two dissimilar metals are chosen as electrodes of a battery (though the above table is not exact for this purpose. See Table of standard electrode potentials).

Simplified Version

The simplified version that is thought in the GCSE and GCE^[1][2] chemistry course, as the basic, are as follows:

Metals	Metal Ion	Reactivity
K	K+	Going from bottom to top, the metals: reactivity increases lose electrons more readily form positive ions more readily becomes a stronger reducing agents A metal 'high up' in the reactivity series: reacts vigourously and quickly with chemicals corrodes easily A metal 'low down' in the reactivity series: doesn't react vigourously and quickly with chemicals doesnt corrodes easily
Na	Na+
Ca	Ca2+
Mg	Mg2+
Al	Al3+
Zn	Zn2+
Fe	Fe2+
Sn	Sn2+
Pb	Pb2+
Fe	Fe2+
H2	H+
Cu	Cu2+
Ag	Ag+
Au	Au3+

Significance

The reactivity series determines qualitatively characteristics such as the reactions with water, air and acids as demonstrated above. However it is defined by the nature of the metals in single displacement reactions.

When a metal in elemental form is placed in a solution of a metal salt it may be, overall, more energetically feasible for this "elemental metal" to exist as an ion and the "ionic metal" to exist as the element. Therefore the elemental metal will 'displace' the ionic metal over time, thus the two swap places. Only a metal higher in the reactivity series will displace another.

References

• ^[1]Science in Focus, Chemistry for GCE 'O' Level by J G R Briggs; Chapter 11 pg 172. Pearson Education South Asia Pte Ltd 2005.
• ^[2]Longman Pocket Study Guide 'O' Level Science-Chemistry by Lim Eng Wah; Chapter 8 pg 190. Pearson Education South Asia Pte Ltd 2005.

External links

• Science Line Chemistry