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Stoichiometry of Chemical Reactions Explained

Apr 7, 2025

Stoichiometric Calculations in Chemical Reactions

Introduction

  • Previous lessons covered:
    • Understanding balanced chemical equations.
    • Writing stoichiometric factors from equations.
    • Simple calculations converting between species in a reaction.
  • Current focus:
    • Practice stoichiometric calculations involving mass, moles, and solution molarity.

Example 1: Sodium Hydroxide and Magnesium Hydroxide

  • Objective: Calculate the mass of sodium hydroxide (NaOH) needed to produce 16 grams of magnesium hydroxide from a given reaction.
  • Steps:
    1. Start with the mass of magnesium hydroxide.
    2. Convert grams to moles using molar mass (58.3 g/mol for Mg(OH)₂).
    3. Use stoichiometric factor from balanced equation (1 mole Mg(OH)₂ : 2 moles NaOH).
    4. Convert moles of NaOH to grams using molar mass (40.0 g/mol for NaOH).
  • Conclusion: 22 grams of NaOH is required.

Stoichiometric Calculation Flow Diagram

  • Relate moles of reactant (A) to moles of product (B) using coefficients from balanced equations.
  • Convert between mass, volume, and moles:
    • Mass to moles: Use molar mass.
    • Volume of a pure substance to moles: Use density.
    • Volume of a solution to moles: Use molarity.
    • Particles to moles: Use Avogadro's number.

Example 2: Sodium Azide and Airbag Inflation

  • Objective: Determine mass of sodium azide (NaN₃) required to produce 73.6 liters of nitrogen gas.
  • Steps:
    1. Start with volume of nitrogen gas.
    2. Convert volume to mass using density (1.25 g/L for N₂).
    3. Convert grams to moles using molar mass (28 g/mol for N₂).
    4. Use stoichiometric factor from balanced equation (3 moles N₂ : 2 moles NaN₃).
    5. Convert moles of NaN₃ to grams using molar mass (65 g/mol for NaN₃).
  • Conclusion: 142 grams of NaN₃ produces 73.6 liters of nitrogen gas, sufficient for airbag inflation.

Key Takeaways

  • Stoichiometric calculations require understanding the relationship between different units (mass, moles, volume).
  • Use balanced chemical equations to determine relationships between reactants and products.
  • Flow diagrams can assist in visualizing complex calculation processes.

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