Lecture Notes on Shifting Equilibrium: Le Chatelier's Principle

Introduction to Le Chatelier's Principle

• Le Chatelier's Principle: If a stress is applied to a system at equilibrium, the system shifts to counteract the stress and achieve a new equilibrium.
• Example Reaction: Nitrogen (N2) + Hydrogen (H2) → Ammonia (NH3)
  • Adding NH3 shifts equilibrium to the left.

Disturbing Equilibrium

• Adding a reactant/product pushes equilibrium to the opposite side.
• Removing a reactant/product pulls equilibrium to the same side.

Example Reactions

• N2O4 (g) ↔ 2 NO2 (g)
  • Adding N2O4 shifts right (push).
  • Adding NO2 shifts left (push).
  • Removing N2O4 shifts left (pull).
  • Removing NO2 shifts right (pull).

Effects of Pressure Changes

• Pressure Increase:
  • Compresses system, shifts to side with fewer moles of gas.
• Pressure Decrease:
  • Expands system, shifts to side with more moles of gas.

Effects of Container Size Changes

• Decreasing container size (increasing pressure) shifts to fewer moles.
• Increasing container size (decreasing pressure) shifts to more moles.

Effects of Temperature Changes

• Endothermic Reactions:
  • Increase temperature favors products (push right).
• Exothermic Reactions:
  • Decrease temperature favors products (push left).

Changing K (Equilibrium Constant)

• Temperature changes alter the equilibrium constant, K.

Role of Catalysts

• Catalysts increase reaction rate without changing equilibrium.

Detailed Examples

1. Volume Decrease with Equal Moles:

   • No equilibrium change.
   • Example reaction: 2 moles reactants ↔ 2 moles products.

2. Example Reactions:

   • Decreasing Volume:
     • Shifts to side with fewer moles of gas.
   • Temperature Increase:
     • Shifts in direction consuming added energy.

Practical Applications

• Hydrazine Production from N2 and H2:
  • Add N2 or H2, decrease volume, or increase temperature to shift equilibrium right.

Specific Examples from Textbook

• Temperature and Volume Changes:
  • Different reactions respond differently based on moles of gases and temperature sensitivity.

Equilibrium and Reaction Processes

• Catalyst Addition: Only speeds up reaching equilibrium.
• Adding NaOH: Shifts equilibrium left, forming more NH3.

Physical Processes

• Boiling Water:
  • Increasing temperature or reducing pressure can shift liquid to gas phase.

Conclusion

• Understanding how different factors affect chemical equilibrium is crucial for predicting and controlling reactions in both laboratory and industrial settings.