CH 20.1-2

Chapter 20.1-2: Electrochemistry Overview

• Focus on the interchange of chemical and electrical energy from redox reactions.

Redox Reactions

• Definition: Redox reactions involve the transfer of electrons, which occur simultaneously for oxidation and reduction.

• Key Terms:

  • Oxidation: Loss of electrons (LEO - Loss Electrons Oxidation)

  • Reduction: Gain of electrons (GER - Gain Electrons Reduction)

  • Oxidizing Agent: Substance that gains electrons; causes oxidation.

  • Reducing Agent: Substance that loses electrons; causes reduction.

Oxidation States

• Used to define oxidation and reduction in reactions.

• Basic rules for assigning oxidation numbers:

  1. Elemental form has an oxidation number of 0.

  2. Monatomic ions equal their charge.

  3. Oxygen is usually -2.

  4. Hydrogen is +1.

  5. Fluorine is always -1; other halogens are usually -1.

  6. Sum of oxidation numbers equals 0 in neutral compounds.

  7. Sum in polyatomic ions equals the ion charge.

Balanced Half-Reactions

• Redox reactions can be separated into oxidation half-reaction and reduction half-reaction.

• Balancing Steps in acidic solutions:

  1. Balance all elements except H and O.

  2. Balance O by adding H2O.

  3. Balance H by adding H+.

  4. Balance charge by adding electrons (e-).

  5. Ensure electrons lost in oxidation = electrons gained in reduction.

  6. Add half-reactions and cancel similar species.

Exercises

• Exercise 20.1.1: Identify oxidation numbers from given compounds.

• Exercise 20.1.2: Identify redox reactions and agents in reactions provided.

• Exercise 20.2.1: Balance a redox equation using the half-reaction method.

• Exercise 20.2.2: Balance another redox equation in acidic solution.

Conclusion

• Understanding the principles of oxidation states and how to balance redox reactions is essential for mastering electrochemistry.