Electrochemistry - AP Chemistry Exam Preparation

Introduction

• Electrochemistry: one of the toughest topics on the AP Chem exam.
• Focus on representations, types, properties of electrochemical cells, and related calculations.
• Thermodynamics also included, as part of Unit 9.

Electrochemical Cells

Types of Cells

• Voltaic Cells (Galvanic)

  • Spontaneous reactions, thermodynamically favorable.
  • E cell is positive, ΔG (free energy) is negative.
  • Equilibrium constant (K) greater than 1.

• Electrolytic Cells

  • Non-spontaneous, require an external power source (battery).
  • E cell is negative, ΔG is positive.
  • Equilibrium constant (K) less than 1.

Key Concepts

• Oxidation occurs at the anode, reduction at the cathode.
• Cell diagrams: Identify the type (voltaic vs electrolytic) by presence of a power source and compartments.

Calculations and Relationships

Important Equations

• Relationship: Positive E cell -> Negative ΔG -> K > 1
• Standard Cell Potential (E⁰ cell): E⁰ cathode - E⁰ anode
• Free Energy (ΔG⁰): ΔG⁰ = -nFE⁰

Cell Diagrams and Equilibrium

• Equilibrium constant (Q) and its role in determining cell potential.
• Non-standard conditions require Q vs K reasoning.

Problem Solving and Practice

Voltaic Cell Diagrams

• Identify anode and cathode.
• Determine standard conditions (1 M concentration, 298 K, 1 atm).

Non-standard Cell Potentials

• Use Q vs K to understand cell behavior under non-standard conditions.
• Smaller Q means higher cell potential in voltaic cells.

Electrolysis and Stoichiometry

Calculations

• Stoichiometry for electron transfer.
• Use Faraday's Law for current calculations.
• Standard reduction potential tables for reaction identification.

Thermodynamics

• Entropy (ΔS): Positive if more moles of gas are produced.
• Melting and Heat Calculations: Use specific heat and heat of fusion.

Practical Tips

• Conductivity: Mobile ions in liquids essential.
• Roles of Solids vs Ions: Solids do not affect cell potential calculations.
• Phase Changes: Require separate calculations for heating and melting.

Exam Strategy

• Use provided formula sheets effectively.
• Practice with AP Daily videos and review sessions.
• Focus on understanding concepts, relationships, and reasoning.

Feedback and Resources

• Provide feedback through the given forms.
• Utilize QR codes for additional resources and practice materials.
• Preparation is key to success.