Lecture on Limiting Reactants and Stoichiometry

Introduction

• Focus on limonene reactants and solving stoichiometry problems involving limiting reactants.

Example 1: Zinc and Hydrochloric Acid Reaction

• Balanced Chemical Equation:
  • Reactants: Zinc (Zn) and Hydrochloric Acid (HCl)
  • Products: Hydrogen gas (H₂) and Zinc Chloride (ZnCl₂)
  • Zn + 2HCl → H₂ + ZnCl₂

Part A

• Given: 12 atoms of Zinc, 8 molecules of HCl.
• Limiting Reactant: HCl
  • Calculated using the lowest quantity per coefficient ratio.
  • Zinc: 12/1 = 12
  • HCl: 8/2 = 4
  • Conclusion: HCl is limiting reactant.

Part B

• Given: 3 moles of Zinc, 4 moles of HCl.
• Limiting Reactant: HCl
  • Zinc: 3/1 = 3
  • HCl: 4/2 = 2
  • Conclusion: HCl runs out first.

Part C

• Given: Grams of Zinc and HCl.
• Steps: Convert grams to moles, then divide by coefficients.
  • Zinc: Molar mass = 65.39
  • HCl: Molar mass = 36.458
  • Zinc moles: 40/65.39 = 0.6117
  • HCl moles: 56/36.458 = 1.536
  • Limiting Reactant: Zinc
  • Moles per coefficient: Zinc = 0.6117, HCl = 0.768

Example 2: Ethane and Oxygen Reaction

• Balanced Chemical Equation:
  • Reactants: Ethane (C₂H₆) and Oxygen gas (O₂)
  • Products: Carbon Dioxide (CO₂) and Water (H₂O)
  • 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O

Part A

• Given: 5 moles of Ethane, 16 moles of O₂.
• Method 1: Lowest quantity per coefficient ratio.
  • Ethane: 5/2 = 2.5
  • O₂: 16/7 = 2.29
• Method 2: Convert moles of reactants to product.
  • Ethane produces 10 moles CO₂.
  • O₂ produces 9.14 moles CO₂.
  • Limiting Reactant: O₂
  • Product Yield: 9.14 moles CO₂

Part B

• Given: 30 grams of Ethane, 84 grams of O₂.
• Conversion Steps:
  • Ethane to water: 53.93g
  • O₂ to water: 40.54g
  • Conclusion: O₂ is limiting reactant, produces 40.5g water.

Key Takeaways

• Limiting reactant is the one that runs out first, determines the maximum amount of product.
• Always compare reactants by converting to moles and using their coefficients for accurate analysis.
• The smaller theoretical yield indicates the limiting reactant and the yield of the reaction.