Reactivity Series

It refers to the reactivity series of metals or elements which are metals. It is also known as the activity series. In this series, the metals are arranged in descending order of their reactivity. It means the more reactive metals come first in this series followed by less reactive metals. So, it is a list of metals arranged in order of decreasing reactivity.

It is generally a vertically presented series that contains the most-reactive elements at the top of the series and the least-reactive elements at the bottom.

The reactivity series tells whether a metal can displace another metal in a displacement reaction or not. The more reactive metal tends to displace less reactive metal in displacement reactions. The reactivity of metals is generally determined by their ability to displace hydrogen gas from water and acids. So, it also tells about the reactivity of metals towards water and acids.

Salient features of reactivity series

• The metals at the top of this series are powerful reducing agents as they tend to lose electrons (oxidised) easily. So, these metals corrode easily.
• As the reactivity decreases the reducing ability of metals also decreases down the series.
• The electro positivity (tendency to lose electrons) of metals also reduces while moving down the activity series of metals.
• The metals placed above the hydrogen produce Hydrogen gas (H₂) when react with dilute HCl or dilute H₂SO₄.
• The metals that are placed above displaces the metals placed below from their salt solutions.
• Metals placed high in the series need more energy for their separation from ores and other compounds.

Although hydrogen is a non-metal, it is placed in the reactivity series of metals. This is because hydrogen helps compare the reactivity of metals. The metals that are located above the hydrogen can displace it from acids such as HCl and H₂SO₄.

The reactivity series not only provides information about the properties and reactivity of metals but also offers various other applications. For example, it can help you predict the outcome of reactions of metals with water, acids and with other metals as described below;

i) Reaction between metals and water

Calcium including the metals that are situated above it in the series react with cold water to form the corresponding metal hydroxide and hydrogen gas. For example, when potassium reacts with water potassium hydroxide and H₂ are produced as shown in the below chemical reaction;

2K + 2H₂O →; 2KOH + H₂

Similarly, we can predict the reaction of other metals with water with the help of reactivity series.

ii) Reaction of metals with acids

Lead including the metals located above it, form salts when react with hydrochloric acid or sulphuric acid; hydrogen gas is also produced. For example, when Zn is located above lead in the series when reacts with sulphuric acid leads to the formation of zinc sulfate and H₂ gas.

Zn + H₂SO₄ → ZnSO₄ + H₂

Similarly, we can predict the reaction of other metals located above lead with acids with the help of reactivity series.

iii) Displacement reaction between metals

The more reactive metals or high ranking metals reduces (donate electrons) the ions of less reactive metals or low ranking metals in the series. This is the reason for the displacement of less reactive metals by more reactive metals in the single displacement reactions. For example, zinc being more reactive than copper displaces copper from copper sulphate as shown in the below reaction

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

So, the reactivity series also tells the outcome of single displacement reactions, which are used to extract metals from their ores.

The reactivity series starts with the cesium metal which means cesium is at the top of the reactivity series or is the most reactive metal of this series. Generally, the alkali metals are the most reactive metals followed by the alkaline earth metals which are followed by transition metals. Whereas, noble metals like silver, gold and platinum are nearly non-reactive.

Reactions used to test reactivity

The following reactions can be used to test the reactivity of metals;

i) Reactions with cold water: The highly reactive metals easily react with cold water to form the metal hydroxide and hydrogen gas. Metals that don't react with water may react with acids.

ii) Reactions with acids: Reactive metals when react with acids produce the metal salt and hydrogen.