Chapter 19: Redox Reactions

Oxidation-Reduction Reaction

A class of chemical reactions involving the transfer of electrons; also known as a redox reaction.

Oxidation

Occurs when an atom loses electrons. Its oxidation number becomes more positive.

Reduction

Occurs when an atom gains electrons, making its oxidation number smaller.

Key Characteristics of Redox Reactions

• Oxidation and reduction always occur simultaneously.
• Electrons lost by one atom are gained by another.
• Only reactions involving changes in oxidation numbers are redox reactions.

Oxidizing and Reducing Agents

Reducing Agent

A substance that causes the reduction of another substance; it is oxidized in the process.

Oxidizing Agent

A substance that causes the oxidation of another substance; it is reduced in the process.

Steps to Balance Redox Reactions

1. Assign oxidation numbers to all atoms.
2. Determine which atoms are oxidized and reduced.
3. Draw lines connecting atoms involved in oxidation and reduction. Write the net oxidation number changes.
4. Balance the magnitude of oxidation number changes using coefficients.
5. Use the conventional inspection method to balance the equation.

Example Problems

Example 19-1

Determine whether a reaction is a redox reaction by analyzing changes in oxidation numbers.

Example 19-2

Identify the reducing agent and oxidizing agent in a redox reaction.

Example 19-4

Balance a redox reaction using the oxidation-number method.

Questions for Students

1. Define oxidation and reduction. How are they related in a redox reaction?
2. Explain the roles of reducing agents and oxidizing agents in redox reactions.
3. Balance the following redox reaction using the oxidation-number method: $\mathrm{Fe}\left({\mathrm{OH}}_2\right)+H_{2}S\to {\mathrm{Fe}}_{2}O+H+S_2$
4. Describe the steps involved in balancing a redox reaction.
5. Provide an example of a redox reaction from daily life, such as rusting or battery operation.