Reactivity Series

What is the Reactivity Series?

The reactivity series of metals, also known as the activity series, refers to the arrangement of metals in the descending order of their reactivities.

The data provided by the reactivity series can be used to predict whether a metal can displace another in a single displacement reaction. It can also be used to obtain information on the reactivity of metals towards water and acids.

A chart of the reactivity series of common metals is provided below.

Metals tend to readily lose electrons and form cations. Most of them react with atmospheric oxygen to form metal oxides. However, different metals have different reactivities towards oxygen (unreactive metals such as gold and platinum do not readily form oxides when exposed to air).

Salient Features

• The metals at the top of the reactivity series are powerful reducing agents since they are easily oxidized. These metals tarnish/corrode very easily.
• The reducing ability of the metals grows weaker while traversing down the series.
• The electro positivity of the elements also reduces while moving down the reactivity series of metals.
• All metals that are found above hydrogen in the activity series liberate H₂ gas upon reacting with dilute HCl or dilute H₂SO₄.
• Metals that are placed higher on the reactivity series have the ability to displace metals that are placed lower from their salt solutions.
• Higher ranking metals require greater amounts of energy for their isolation from ores and other compounds.

Another important feature of the activity series is that while travelling down the series, the electron-donating ability of the metals reduces.

Long Tabular Form of the Reactivity Series

The reactivities of metals are tabulated below (in the descending order) along with their corresponding ions. Note that the metals in Red react with cold water, those in Orange cannot react with cold water but can react with acids, and those in Blue only react with some strong oxidizing acids.

Despite being a non-metal, hydrogen is often included in the reactivity series since it helps compare the reactivities of the metals. The metals placed above hydrogen in the series can displace it from acids such as HCl and H₂SO₄ (since they are more reactive).

Important uses of Reactivity Series

Apart from providing insight into the properties and reactivities of the metals, the reactivity series has several other important applications. For example, the outcome of the reactions between metals and water, metals and acids, and single displacement reactions between metals can be predicted with the help of the activity series.

Reaction Between Metals and Water

Calcium and the metals that are more reactive than calcium in the reactivity series can react with cold water to form the corresponding hydroxide while liberating hydrogen gas. For example, the reaction between potassium and water yields potassium hydroxide and H₂ gas, as described by the chemical equation provided below.

2K + 2H₂O → 2KOH + H₂

Therefore, the reactivity series of metals can be used to predict the reactions between metals and water.

Reaction Between Metals and Acids

Lead and the metals ranking above lead on the activity series form salts when reacted with hydrochloric acid or sulphuric acid. These reactions also involve the liberation of hydrogen gas. The reaction between zinc and sulphuric acid is an example of such a reaction. Here, zinc sulfate and H₂ gas are formed as products. The chemical equation is:

Zn + H₂SO₄ → ZnSO₄ + H₂

Thus, the reactions between metals and some acids can be predicted with the help of the reactivity series.

Single Displacement Reactions Between Metals

The ions of low ranking metals are readily reduced by high ranking metals on the reactivity series. Therefore, low ranking metals are easily displaced by high ranking metals in the single displacement reactions between them.

A great example of such a reaction is the displacement of copper from copper sulfate by zinc. The chemical equation for this reaction is given by:

Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)

This concept has several practical applications in the extraction of metals. For example, titanium is extracted from titanium tetrachloride via a single displacement reaction with magnesium. Thus, the reactivity series of metals can also be used to predict the outcome of single displacement reactions.

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