Chem 115 Lecture - Session 8.2

Introduction

• This session focuses on key concepts of chemical equilibrium and reaction rates.
• Discussion includes definitions, examples, and mathematical representations.

Chemical Equilibrium

• Definition: A state where the concentrations of all reactants and products remain constant over time.
• Dynamic Equilibrium: The rate of the forward reaction equals the rate of the reverse reaction.

Factors Affecting Equilibrium

• Concentration: Changes can shift equilibrium.
• Temperature: Increasing temperature generally favors endothermic reactions.
• Pressure: Affects reactions involving gases; increasing pressure favors the side with fewer moles of gas.

Equilibrium Constant (K)

• Expression: K = [Products]/[Reactants]
• Significance:
  • K > 1: Products favored at equilibrium.
  • K < 1: Reactants favored at equilibrium.
• Types:
  • Kc: Concentration-based
  • Kp: Pressure-based, used for gaseous reactions

Reaction Rates

• Definition: Change in concentration of a reactant or product per unit time.

Factors Influencing Reaction Rates

• Concentration: Higher concentration generally increases rate.
• Temperature: Higher temperature increases kinetic energy, thus increasing rate.
• Catalysts: Speed up reactions without being consumed.

The Rate Law

• General Form: Rate = k[A]^m[B]^n
• k: Rate constant
• m, n: Reaction order with respect to each reactant

Reaction Mechanisms

• Definition: Step-by-step sequence of elementary reactions.
• Intermediate: Species that appear in the mechanism but not in the overall balanced equation.
• Rate-Determining Step: Slowest step in the mechanism which determines the rate of the overall reaction.

Conclusion

• Understanding equilibrium and reaction rates is crucial in predicting the behavior of chemical reactions under different conditions.
• The concepts of K and reaction mechanisms are essential in both academic and practical chemistry applications.

Study Tips

• Practice setting up and solving equilibrium expressions.
• Work on identifying reaction orders and calculating rates.
• Familiarize yourself with common catalysts and their effects on reaction rates.