Types of Redox Reactions | Class 11 Chemistry

Types of Redox Reactions

Classification & Examples | Class 11 Chemistry

1. Introduction

Redox reactions involve the transfer of electrons, leading to a change in the oxidation state of species. They can be classified into distinct types based on how reactants combine or break down.

2. Combination Reactions

A reaction in which two atoms or molecules combine to form a third molecule.

                    Condition: For it to be a redox reaction, at least one of the reacting species must be in its elemental form.
                

$$ C(s) + O_2(g) \xrightarrow{\Delta} CO_2(g) $$

Carbon (0) is oxidized to +4, and Oxygen (0) is reduced to -2.

3. Decomposition Reactions

A reaction where a molecule breaks down into two or more components. At least one product must be in the elemental state.

$$ 2H_2O(l) \xrightarrow{\text{Electric Current}} 2H_2(g) + O_2(g) $$

Note: Not all decompositions are redox. Example: $CaCO_3 \rightarrow CaO + CO_2$ is not redox (no change in Oxidation Number).

4. Displacement Reactions

An atom or ion in a compound is replaced by an atom or ion of another element ($X + YZ \rightarrow XZ + Y$).

A. Metal Displacement

A metal in a compound is displaced by another metal in the elemental state.

$$ CuSO_4(aq) + Zn(s) \rightarrow ZnSO_4(aq) + Cu(s) $$

Zinc (0) oxidizes to +2; Copper (+2) reduces to 0.

B. Non-metal Displacement

Usually involves displacement of Hydrogen or Oxygen.

$$ Zn(s) + 2HCl(aq) \rightarrow ZnCl_2(aq) + H_2(g) $$

5. Disproportionation Reactions (Auto-Redox)

A reaction in which the same element in a single oxidation state is simultaneously oxidized and reduced.

                    Condition: The element must exist in at least three oxidation states. The reacting state must be intermediate.
                

$$ 2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2(g) $$

Oxygen in $H_2O_2$ is -1. It reduces to -2 ($H_2O$) and oxidizes to 0 ($O_2$).

6. Comproportionation Reactions

Also known as Synproportionation. It is the reverse of Disproportionation.

                    Definition: Two reactants containing the same element in different oxidation states react to form a product where the element has an intermediate oxidation state.
                

$$ Ag^{2+}(aq) + Ag(s) \rightarrow 2Ag^+(aq) $$

Here, Silver in (+2) and (0) states combine to form Silver in (+1) state.

Another Example: Reaction of Iodide and Iodate ions in acidic medium:

$$ IO_3^- (+5) + 5I^- (-1) + 6H^+ \rightarrow 3I_2 (0) + 3H_2O $$

Practice Quiz

Test your ability to classify redox reactions.

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