Lecture Notes: Chemical Equilibrium and Le Chatelier's Principle

Introduction

• Lecture on physics and chemistry, focusing on chemical equilibrium.
• Contact for feedback: [email protected]

Chemical Equilibrium

• Definition: A state where the rate of the forward reaction equals the rate of the reverse reaction.
• Occurs in a closed system where no reactants or products escape.
• Dynamic Equilibrium: Continuous forward and reverse reactions at equal rates.

Factors Affecting Chemical Equilibrium

1. Concentration
   • Affects gases and aqueous solutions only.
   • Increasing concentration disturbs equilibrium, leading to shifts to oppose the change.
2. Temperature
   • Involves endothermic and exothermic reactions.
   • Increase in temperature favors endothermic reactions.
   • Decrease in temperature favors exothermic reactions.
3. Pressure
   • Affects gases only.
   • Increase in pressure favors the side with fewer moles of gas.
   • Decrease in pressure favors the side with more moles of gas.

Le Chatelier’s Principle

• States that if a change in concentration, temperature, or pressure is applied to a system at equilibrium, the system will adjust to oppose the change and a new equilibrium will be established.
• Catalyst Impact: Does not affect equilibrium as it speeds up both forward and reverse reactions equally.

Illustrative Model: Seesaw Analogy

• Adding mass (child) to one side of a seesaw disrupts balance, requiring a shift (movement of a ball) to restore equilibrium.
• Removal of mass leads to a shift towards the side where mass was removed.

Application of Le Chatelier’s Principle

• Concentration: When more of a reactant or product is added, the system shifts away to restore equilibrium; removing shifts towards the removal.
• Temperature:
  • Exothermic Reactions (ΔH < 0): Adding heat shifts equilibrium towards reactants.
  • Endothermic Reactions (ΔH > 0): Adding heat shifts equilibrium towards products.
• Pressure:
  • Increasing pressure shifts towards the side with fewer moles of gas.
  • Decreasing pressure shifts towards the side with more moles of gas.

Examples

• N2 + 3 H2 ⇌ 2 NH3
  • Adding N2 shifts equilibrium to the right, increasing NH3.
  • Removing N2 shifts equilibrium to the left, decreasing NH3.
• CaCO3 ⇌ CaO + CO2 (Endothermic)
  • Increase in temperature favors forward reaction, increasing CaO and CO2.
  • Increase in pressure favors reverse reaction due to zero moles of gas on left.

Conclusion

• Le Chatelier's Principle helps predict the direction of equilibrium shift in response to changes in concentration, temperature, and pressure.
• Future sessions will focus on applying these principles in exam situations.
• Feedback and questions encouraged; contact via email for further clarification.