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Stoichiometry

Stoichiometry is the calculation of quantities of reactants and products in a chemical reaction based on the balanced chemical equation.

Key Concepts​

  • Mole Ratios: Derived from the coefficients in a balanced equation
  • Limiting Reactant: Reactant that determines the maximum amount of product
  • Excess Reactant: Reactant left over after the reaction is complete
  • Theoretical Yield: Maximum amount of product predicted by stoichiometry
  • Actual Yield: Amount of product actually obtained
  • Percent Yield: (Actual Yield / Theoretical Yield) × 100%

Steps to Solve Stoichiometry Problems​

  1. Write and balance the chemical equation.
  2. Convert known quantities to moles.
  3. Use mole ratios to find moles of desired substance.
  4. Convert moles back to grams, liters, or molecules as needed.
  5. Check calculations and units for consistency.

Example​

Given: 2 H₂ + O₂ → 2 H₂O

  • If 4 moles of H₂ react with 2 moles of O₂:
    • H₂: 4 moles × (2 moles H₂O / 2 moles H₂) = 4 moles H₂O
    • O₂: 2 moles × (2 moles H₂O / 1 mole O₂) = 4 moles H₂O
  • Both reactants are perfectly stoichiometric; 4 moles of water form.

Importance​

  • Predicts amounts of reactants needed and products formed
  • Essential for chemical manufacturing, lab experiments, and chemical analysis

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