Reactivity Series: A Comprehensive Guide

The Reactivity Series

Definition

The reactivity series is an arrangement of metals in descending order of their reactivity. This order is determined by how vigorously metals react with water and dilute acids. It helps predict the outcome of displacement reactions.

Factors Affecting Reactivity

  1. Ionization Energy: Metals with lower ionization energies tend to be more reactive because they lose electrons more easily.

  2. Atomic Size: Larger atomic size generally correlates with higher reactivity due to weaker attraction between the nucleus and the outer electrons.

  3. Electronic Configuration: Metals that can easily achieve a stable electronic configuration (e.g., by losing one or two electrons) are often more reactive.

The Reactivity Series (Order of Elements)

The typical reactivity series includes the following elements in decreasing order of reactivity:

Potassium > Sodium > Lithium > Calcium > Magnesium > Aluminium > Zinc > Iron > Tin > Lead > Hydrogen > Copper > Silver > Gold > Platinum

*Note: Hydrogen is included for reference as it participates in reactions with acids.

Reaction with Water

Very Vigorous Reaction

  • Elements: Potassium, Sodium, Lithium

  • These metals react very vigorously with water, forming the metal hydroxide and releasing hydrogen gas and heat. The reactions are exothermic and can be explosive.

  • Example equations:

    • 2K(s) + 2H2O(l) \longrightarrow 2KOH(aq) + H2(g) + Heat

    • 2Na(s) + 2H2O(l) \longrightarrow 2NaOH(aq) + H2(g) + Heat

    • 2Li(s) + 2H2O(l) \longrightarrow 2LiOH(aq) + H2(g) + Heat

Slow Reaction

  • Elements: Calcium, Magnesium

  • These metals react slowly with cold water (magnesium reacts very slowly) to form the metal hydroxide and hydrogen gas. Magnesium’s reaction is significantly enhanced in hot water.

  • Example equations:

    • Ca(s) + 2H2O(l) \longrightarrow Ca(OH)2(aq) + H_2(g)

    • Mg(s) + 2H2O(l) \longrightarrow Mg(OH)2(aq) + H_2(g)

Reaction with Steam

  • Elements: Aluminium, Zinc, Iron

  • These metals do not react with cold water but react with steam to form the metal oxide and hydrogen gas. The metal oxide forms a protective layer that inhibits further reaction.

  • Example equations:

    • 2Al(s) + 3H2O(g) \longrightarrow Al2O3(s) + 3H2(g)

    • Zn(s) + H2O(g) \longrightarrow ZnO(s) + H2(g)

    • Fe(s) + H2O(g) \longrightarrow FeO(s) + H2(g)

No Reaction

  • Elements: Tin, Lead, Copper, Silver, Gold, Platinum

  • These metals do not react with water or steam due to their low reactivity.

Reaction with Dilute Acids

Violent Reaction

  • Elements: Potassium, Sodium, Lithium, Calcium

  • These elements react with dilute acids in a very violent and dangerous manner, typically not done in school labs due to the risk of explosion. These reactions produce metal salts and hydrogen gas.

  • Example equations:

    • 2K(s) + 2HCl(aq) \longrightarrow 2KCl(aq) + H_2(g)

    • 2Na(s) + H2SO4(aq) \longrightarrow Na2SO4(aq) + H_2(g)

    • Ca(s) + 2HNO3(aq) \longrightarrow Ca(NO3)2(aq) + H2(g)

Moderate Reaction

  • Elements: Magnesium, Aluminium, Zinc, Tin

  • These elements react reasonably well with dilute acids, with reactivity decreasing down the series. The reactions are controlled to produce metal salts and hydrogen gas.

  • Example equations:

    • Mg(s) + 2HCl(aq) \longrightarrow MgCl2(aq) + H2(g)

    • Zn(s) + H2SO4(aq) \longrightarrow ZnSO4(aq) + H2(g)

    • Sn(s) + 2HNO3(aq) \longrightarrow Sn(NO3)2(aq) + H2(g)

No Reaction

  • Elements: Lead, Copper, Silver, Gold, Platinum

  • These elements do not react with dilute acids because they are below hydrogen in the reactivity series.

Displacement Reactions

Definition

A displacement reaction is one in which a more reactive metal displaces a less reactive metal from a compound. This is a redox reaction where the more reactive metal loses electrons and the less reactive metal gains electrons.

Explanation

A metal higher up in the reactivity series will 'push out' a metal that is lower in the series from its compound. The driving force is the difference in the stability of the metal ions in solution.

Application

Displacement reactions can be used to deduce the position of a metal within the reactivity series using reactions between metals and their oxides or salts in aqueous solutions. This is useful in metallurgy for extracting metals from their ores.

Example 1: Aluminium and Iron Oxide

  • Aluminium powder reacts violently with iron oxide in the thermite reaction.

  • 2Al(s) + Fe2O3(s) \longrightarrow Al2O3(s) + 2Fe(s)

Example 2: Iron and Copper Sulphate

  • Iron is higher than copper in the reactivity series, so it displaces copper from copper sulphate solution.

  • CuSO4(aq) + Fe(s) \longrightarrow FeSO4(aq) + Cu(s)

Predicting Displacement Reactions

  • If a metal is higher in the reactivity series than the metal in the solution, a displacement reaction will occur.

  • If a metal is lower in the reactivity series than the metal in the solution, no displacement reaction will occur.

Metal

Solution

Displacement Happen?

Lead

Iron sulphate

NO

Lead

Copper sulphate

YES

Iron

Zinc sulphate

NO

Tin

Copper sulphate

YES

Oxidation and Reduction

Definitions of Oxidation

  1. Addition of oxygen to a substance

  2. Removal of hydrogen from a substance

  3. Loss of electrons from a substance (OIL - Oxidation Is Loss)

  • Examples of oxidation:

    • S(s) + O2(g) \longrightarrow SO2(g)

    • 2CO(g) + O2(g) \longrightarrow 2CO2(g)

Definitions of Reduction

  1. Removal of oxygen from a substance

  2. Addition of hydrogen to a substance

  3. Gain of electrons by a substance (RIG - Reduction Is Gain)

  • Examples of reduction:

    • CuO(s) + H2(g) \longrightarrow Cu(s) + H2O(g)

    • Fe2O3(s) + 3CO(g) \longrightarrow 2Fe(s) + 3CO_2(g)