AP Chemistry Unit 9 Review: Thermodynamics and Electrochemistry

Lecturer Introduction

• Lecturer: Jeremy Krug
• Focus: Thermodynamics and Electrochemistry
• Resources for further study: UltimateReviewPacket.com

Entropy Overview

• Entropy is the measure of disorder in a system.
• Solid: Lowest entropy (compact, not dispersed).
• Liquid: Higher entropy than solids.
• Aqueous Solutions: Higher entropy than liquids.
• Gas: Highest entropy.
• Increase in temperature or volume increases entropy.
• Chemical Reactions:
  • Increase in entropy: solid to gas conversion, or increase in number of gas molecules.
  • Decrease in entropy: decrease in number of gas molecules.

Calculating Entropy

• Calculate entropy change: Sum of entropies of products - sum of entropies of reactants.

Thermodynamic Favorability

• Gibbs Free Energy (ΔG): Measure of favorability.
  • ΔG < 0: Thermodynamically favored.
  • ΔG > 0: Not favored.

Standard Conditions

• Standard conditions are 25°C, 1 atm, 1 mole/L.

Calculating ΔG

• Method 1: Sum of Gibbs Free Energies of products - sum of Gibbs Free Energies of reactants.
• Method 2: ΔG = ΔH - TΔS (ensure unit consistency).

Reaction Conditions

• Exothermic & Increasing Entropy (ΔH < 0, ΔS > 0): Favored at all temperatures.
• Endothermic & Decreasing Entropy (ΔH > 0, ΔS < 0): Not favored at any temperature.
• ΔH > 0, ΔS > 0: Favored at high temperatures.
• ΔH < 0, ΔS < 0: Favored at low temperatures.

Kinetic Control

• Thermodynamically favored reactions can have slow rates due to high activation energy.

Gibbs Free Energy & Equilibrium Constant

• ΔG = -RTln(K) (R = 8.314 J/mol·K).
• Thermodynamically favored reactions: ΔG < 0, K is large.
• Non-favored reactions: ΔG > 0, K is small.

Ionic Compounds

• Example: KCl dissolution is thermodynamically favored due to positive entropy change counteracting positive enthalpy change.

Coupled Reactions

• Unfavored reactions can occur with input of energy or coupling with a favored reaction.

Galvanic Cells

• Galvanic cells (batteries) are thermodynamically favored.
• Key components: Anode (oxidation), Cathode (reduction).
• Electron flow: Anode to Cathode.
• The salt bridge maintains charge balance.
• Cell potential calculated using reduction potentials.
• ΔG of cell = -nFE (Faraday’s constant = 96,485 C/mol).

Non-Standard Conditions

• Use the Nernst Equation for changing conditions.
• Changes in concentration affect cell voltage.

Electrolytic Cells

• Non-favored processes driven by external power.
• Used in metal plating.
• Current (amps) = Charge (coulombs) / Time (seconds).
• Stoichiometry used to convert charge to mass.

Conclusion

• Encouragement to engage with further resources and study materials for comprehensive exam preparation.