AP Chemistry Unit 5: Chemical Kinetics

Introduction

• Presenter: Jeremy Krug
• Review of AP Chemistry Unit 5 covering Chemical Kinetics.
• Kinetics: Study of the rate of chemical reactions.

Factors Affecting Reaction Rates

1. Concentration of Reactants
2. Particle Size of Reactants
3. Temperature
4. Presence of a Catalyst

Reaction Rates and Stoichiometry

• Relative rates can be determined from balanced chemical equations.
• Example: Reaction (2 \text{NO} + \text{O}_2 \rightarrow 2 \text{NO}_2)
  • Rate of disappearance of NO = Rate of appearance of NO2
  • Rate of disappearance of O2 is half that of NO.
• Reaction rates typically measured in moles per liter per second.

Rate Laws

• General Form: ( \text{Rate} = k [\text{Reactant}_1]^x [\text{Reactant}_2]^y )
  • (k): Rate constant
  • (x, y): Orders determined experimentally
• Example with experimental data:
  • For ClO2, use experiments where only ClO2 changes.
  • Order determined by changes in concentration and rate.
• Overall Order: Sum of individual orders.

Graphical Determination of Reaction Order

• Make graphs for:
  1. Time vs. Concentration
  2. Time vs. Natural Log of Concentration
  3. Time vs. Reciprocal of Concentration
• Straight Line Interpretation:
  • Concentration vs. Time: Zero Order
  • Natural Log vs. Time: First Order
  • Reciprocal vs. Time: Second Order
• Slope of straight line = Rate constant

Integrated Rate Laws

• Relates rate constant, initial concentration, time, and remaining concentration.
• Half-life for First-Order Reactions:
  • ( t_{1/2} = \frac{0.693}{k} )_

Multi-step Reactions and Mechanisms

• Reactions may involve multiple steps.
• Rate Laws for Elementary Steps:
  • Example: (k_1[\text{NO}][\text{Cl}_2])
• Activation Energy and Molecular Collisions:
  • Collisions must have sufficient energy and correct orientation._

Energy Graphs and Reaction Profiles

• Key Points on Energy Graphs:
  • Activation energy
  • Change in enthalpy ((\Delta H))
  • Exothermic vs. Endothermic

Arrhenius Equation

• Relates rate constants at different temperatures to activation energy.
• Graph: Reciprocal of Temperature vs. Natural Log of Rate Constant
• Slope = (-\frac{\text{Activation Energy}}{R})

Reaction Intermediates and Catalysts

• Intermediates: Temporary molecules in reactions.
• Catalysts: Speed up reactions without being consumed.
  • Lower activation energy
  • Surface catalysts allow bonding with surface.

Conclusion

• More resources and detailed reviews available at Ultimate Review Packet dot com.
• Full 30-minute review video for Unit 5 available.

Note: This summary is based on a 10-minute review and does not cover all details. For comprehensive understanding, refer to full resources.