Lecture Notes: Chemical Reactions and Kinetics

Overview

• Review of Chapter 7: Describing and categorizing chemical reactions
• Focus of current chapter: Reaction mechanisms, kinetics, and reversible reactions leading to equilibrium

Collision Theory

• Reactions occur due to molecular collisions
• Requirements for successful collisions:
  • Correct orientation
  • Sufficient energy (activation energy)
• Example: Nitrogen and oxygen molecules forming nitrogen monoxide

Activation Energy

• Necessary energy to break bonds and form products
• Seen in reaction coordinate diagrams as a 'bump'
• Even exothermic reactions require it, e.g., combustion needs a spark

Measuring Reaction Rates

• Rate measured by product formation per unit time or reactant consumption
• Factors affecting rate:
  • Temperature
  • Concentration
  • Catalysts

Factors Influencing Reaction Rate

• Temperature: Higher temperature increases kinetic energy, leading to more successful collisions
• Concentration: Increasing concentration raises chances of collisions
• Catalysts: Speed up reactions without being consumed by lowering activation energy

Reversible Reactions and Equilibrium

• Reversible reactions can reach equilibrium where forward and reverse rates are equal
• Equilibrium doesn't mean equal concentrations of reactants and products
• Dynamic equilibrium: Continuous reactions maintaining constant concentrations

Writing Equilibrium Expressions

• Use equilibrium constant (K or Kc)
• Expression: Products over reactants, with each raised to the power of their coefficients
• Exclude solids and liquids from equilibrium expressions

Calculating Equilibrium Constants

• Given concentrations at equilibrium, plug into equilibrium expression to solve for Kc
• Large Kc indicates product-favored equilibrium; small Kc indicates reactant-favored

Le Chatelier's Principle

• Systems at equilibrium counteract changes to restore equilibrium
• Changes can include:
  • Concentration: Adding/removing reactants/products shifts equilibrium
  • Pressure (for gases): Change in volume shifts equilibrium toward fewer/more moles of gas
  • Temperature: Treated as a product/reactant, affects equilibrium based on exothermic/endothermic nature

Solubility Product (Ksp)

• Describes equilibrium of sparingly soluble salts
• Expression involves concentrations of resulting ions
• Calculating Ksp from solubility: Use stoichiometry to find ion concentrations

Applications and Examples

• Practicing equilibrium expression writing and solving for Kc or Ksp
• Using Le Chatelier's Principle to predict equilibrium shifts
• Calculating molar solubility from Ksp values

Conclusion

• Practice problems recommended to grasp equilibrium concepts
• Further reading in textbook, specifically sections on equilibria in acids and bases (Chapter 12)
• Reach out with questions for further clarification