Understanding Chemical Equilibrium and Le Chatelier's Principle

Introduction

• Chemical systems establish equilibrium by balancing rates of forward and reverse reactions.
• Equilibrium in chemistry is akin to personal balance in life, where systems adjust to stress.

Le Chatelier's Principle

• Definition: Chemical systems shift to alleviate stress.
• Types of Stress on Chemical Systems:
  1. Changes in concentration
  2. Changes in temperature
  3. Changes in pressure
• Reaction systems at equilibrium respond to these stressors to maintain balance.

Changes in Concentration

• Adding a substance shifts the equilibrium away from the addition.
• Removing a substance results in a shift to replace the removed component.
• Example: Decomposition of hydrogen iodide into hydrogen and iodine.
  • Adding hydrogen iodide shifts equilibrium to the right (toward products).
  • Adding iodine shifts equilibrium to the left (toward reactants).

Changes in Pressure

• Only affects systems with gaseous reactants or products.
• Solids and liquids are not considered as they are incompressible.
• Pressure changes can be viewed as concentration changes.
• Steps to analyze pressure changes:
  • Check for presence of gases.
  • Determine high and low pressure sides by comparing moles of gas.
• Example: Haber Process (production of ammonia from hydrogen and nitrogen gas)
  • Reactant side has more moles (4) compared to product side (2).
  • Increasing pressure shifts equilibrium towards the side with fewer moles of gas.

Changes in Temperature

• Impact varies between endothermic and exothermic reactions.
• Endothermic reactions (ΔH > 0): Heat is absorbed, can be treated as a reactant.
  • Cooling shifts equilibrium to left (towards reactants).
• Exothermic reactions (ΔH < 0): Heat is released, can be treated as a product.
  • Cooling shifts equilibrium to right (towards products).
• Temperature changes affect the equilibrium constant (K) by altering molecular energetics.

Summary

• Equilibrium is a dynamic state with balanced rates of reaction.
• Chemical systems under stress adapt to regain equilibrium as per Le Chatelier's Principle.
  • Adding a substance causes a system shift away from it.
  • Removing a substance causes a system shift toward it.
• Understanding these principles allows prediction and influence over chemical reactions, similar to maintaining balance in life.