March 21 Le Chatlies Principle Chem Lecture

Office Hours and Help Availability

  • Office hours: today between 11:30 AM - 12:30 PM
  • Open to questions about homework due today or topics you're struggling with.
  • Alternative help:
  • Call session today at 2 PM.
  • Email can be used to schedule help for next week if you can't meet during office hours.

Exam Information

  • Next exam: March 31
  • Coverage:
  • Chapter 14.7: Kinetics of reaction mechanisms.
    • Note: Integrated rate laws will not be included.
    • Answer questions regarding reaction mechanisms, including some information on catalysis.
  • Chapters 15 & 16:
    • Focus on thermodynamics: entropy, Gibbs free energy, predicting spontaneity.
  • Additional Resources:
  • Exam resources page and practice exam posted on Canvas.
  • Recommended to take the practice exam under timed conditions after studying.

Gibbs Free Energy (ΔG)

  • Last class covered significant equations relating ΔG and K:
  • Relationship: ΔG° = -RT ln(K)
  • ΔG° < 0 indicates K > 1
  • ΔG° > 0 indicates K < 1
  • Transition to non-standard ΔG (ΔG) calculations:
  • ΔG = ΔG° + RT ln(Q)
  • Q: Reaction quotient, reflecting concentrations not balanced at equilibrium.
  • Concept:
  • If ΔG is negative, energy is released. If positive, energy is absorbed during the reaction.

Reaction Equilibrium Shifts

Equilibrium Disturbances

  • Le Chatelier's Principle:
  • Describe how systems at equilibrium respond to changes to reestablish balance.
  • Four main disturbances:
    1. Increasing reactant concentration:
      • Shifts reaction right (toward products).
    2. Increasing product concentration:
      • Shifts reaction left (toward reactants).
    3. Decreasing reactant concentration:
      • Shifts reaction left (to replenish reactants).
    4. Decreasing product concentration:
      • Shifts reaction right (to replenish products).
  • Important Note:
  • Adding/removing solids or liquids does not affect equilibrium.

Changing Pressure and Volume in Gaseous Reactions

  • Effect of Pressure:
  • Changing pressure affects gaseous systems; higher pressure favors side with fewer moles.
  • Lower volume increases pressure and pushes equilibrium toward the side with fewer gas moles.
  • Effect of Volume Increase:
  • Enlarging the volume shifts equilibrium towards the side with more moles of gas.
  • No Effect on K:
  • Changes in pressure/volume do not alter the equilibrium constant (K); only temperature changes affect K values.

Summary of Reaction Shifts When Adding/Removing Components

  • If you add/react product, equilibrium shifts accordingly to achieve balance.
  • Used chemical equations to determine mole changes and predict shifts accurately when adjusting concentrations.