Chemical Synthesis: Multi-Step Reactions

Introduction

• Lecturer: Mr. Lim
• Topic: Multi-step reactions in chemical synthesis

What are Multi-Step Reactions?

• Chemical reactions completed over multiple steps
• Calculations can be done for each step individually or combined
• Stoichiometry applies across individual equations (horizontally), not from one equation to another

Key Concepts

• Stoichiometry in Multi-Step Reactions
  • Example: Producing ammonia (NH₃) and then ammonium nitrate (NH₄NO₃)
  • 1 mole of nitrogen gas (N₂) -> 2 moles of ammonia (NH₃)
  • 2 moles of NH₃ -> 2 moles of NH₄NO₃ (1:1 ratio)
  • Stoichiometry does not carry over vertically between reactions
• Combining Multi-Step Equations
  • Similar to redox half-equations
  • Multiply equations so common reactant/product has the same coefficient
  • Example: Combining equations with reactant/product C
    • Multiply first equation to match common reactant/product
    • Combine and cancel out to simplify
  • This method is complex and might be easier to handle step-by-step

Practical Examples

• Example Calculation:
  • 6.3 moles of H₂ -> 4.2 moles of NH₃ -> 4.2 moles of NH₄NO₃
  • Multi-step calculations combining equations
  • Final product ratio: 12:1 (e.g., 4 moles of A -> 1/3 moles of G)

Rate-Determining Step

• The slowest reaction determines the overall rate of the multi-step reaction
• Rate-determining step produces the least amount of product in a set time

Conclusion

• Introduction to multi-step reactions
• Importance of recognizing rate-determining steps
• Next video: Rate and yield optimization

Farewell

• Mr. Lim's sign-off: "Adios"