Le Chatelier's Principle

Introduction

• Le Chatelier's principle addresses how a chemical system at equilibrium responds to disturbances.
• A system not at equilibrium will move toward equilibrium.
• When disturbed, the system shifts to minimize the disturbance and return to equilibrium.
• Equilibrium constant (K, Kc, Kp) remains constant at a given temperature.

Disturbances and Response

Adding or Removing Reactants or Products

• If a product is added, the reaction shifts to consume the added product (shifts left).
• If a product is removed, the reaction shifts to produce more of that product (shifts right).
• If a reactant is added, the reaction shifts to consume the added reactant (shifts right).
• If a reactant is removed, the reaction shifts to produce more of that reactant (shifts left).

Changes in Pressure and Volume

• Pressure and Volume Relationship: Inverse relationship as per the ideal gas law.
  • Decrease volume -> Increase pressure.
  • Increase volume -> Decrease pressure.
• Reaction Response to Volume/Pressure Changes:
  • Increase in pressure (decrease in volume) favors the side with fewer moles of gas.
  • Decrease in pressure (increase in volume) favors the side with more moles of gas.

Special Cases

• Reactions with equal moles of gas on both sides do not respond to pressure/volume changes.
• Inert gas addition affects total pressure but not the partial pressure of reacting gases.

Temperature Changes

• Exothermic Reactions: Heat is a product.
  • Increase in temperature shifts reaction left; decreases the equilibrium constant.
  • Indicated by delta H < 0.
• Endothermic Reactions: Heat is a reactant.
  • Increase in temperature shifts reaction right; increases the equilibrium constant.
  • Indicated by delta H > 0.
• Temperature changes alter the actual value of the equilibrium constant.

Summary

• Understanding how equilibrium shifts help predict reaction behavior under different conditions.
• Equilibrium constants are temperature-dependent and can change with temperature.
• Further study will involve calculating the impact of temperature changes on equilibrium constants.