Work Energy Theorem and Reaction Rates

Chemical Reaction Basics

• Chemical Reaction: Process where reactants convert to products.
  • Involves breaking intra-molecular bonds and forming new ones.
  • Results in energy changes in the system.
• Conservation: Atoms are conserved, but molecular composition changes.
  • Example: H and O atoms rearrange from water molecules to form different products.

Energy Changes in Reactions

• Potential Energy Diagram: Used to represent energy changes.
• Activation Energy (Ea): Minimum energy needed for reaction.
• Enthalpy Change (ΔH): Net energy change (heat transfer) in reaction.

Reaction Rates

• Definition: Speed of the reaction, measured as change in concentration over time.
• Graph Trends: Rate affects speed but not the end state of the reaction.

Factors Affecting Reaction Rates

1. Concentration
   • Increased concentration increases collision frequency.
2. Catalyst
   • Lowers activation energy, providing an alternative reaction pathway.
3. Division of State
   • Increased surface area leads to higher collision frequency.
4. Nature of Reactant
   • Some reactants react faster due to inherent properties.
5. Temperature
   • Higher temperature increases kinetic energy and successful collisions.

Example Reactions and Calculations

Calcium Carbonate and Hydrochloric Acid Reaction

• Exothermic Reaction: ΔH < 0, energy released.
• Rate Calculation: Mass of reactants used to calculate rate.
  • Example: From 2g to 0.25g in 30s, rate is 0.06 g/s.

Investigations and Exam Questions

• Controlled Variables: Concentration of acid, physical properties of reactants.
• Conclusion from Graphs: Reaction rate increases with temperature.
• Collision Theory Explanation: More kinetic energy leads to more effective collisions.

Maxwell-Boltzmann Distribution and Potential Energy Diagrams

• Temperature Effects: Higher temperatures shift distribution curves right.
• Catalyst Role: Lowers activation energy, increasing reaction rate.

Past Exam Question Highlights

• Reaction of Zinc with Hydrochloric Acid: Investigating reaction rate factors.
• Sodium Thiosulphate Reaction: Analyzing results from experimental investigations.
• Graph Analysis: Using graphs to calculate reaction rates and interpret results.

Example Calculations

• Average Rate Calculation: Using mass or volume changes over time.
• Collision Theory Application: Explaining differences in reaction rates based on reactant conditions and properties.