Introduction to Stoichiometry

Types of Conversions

• Three types of conversions in chemical reactions:
  1. Moles of substance A to moles of substance B
  2. Moles of substance A to grams of substance B or grams of substance A to moles of substance B
  3. Grams of substance A to grams of substance B
• Steps involved:
  • First type: Single step
  • Second type: Two steps
  • Third type: Three steps

Example Problems

Problem 1: Sulfur Dioxide Reaction

• Reaction: SO2 + O2 → SO3

• Balanced Equation: 2 SO2 + O2 → 2 SO3

• Given: 3.4 moles of SO2

• Conversion to SO3:

  • Mole ratio (M ratio): 2 SO2 : 2 SO3 (1:1 ratio)
  • Calculation: 3.4 moles SO2 → 3.4 moles SO3

• Follow-up Problem:

  • Given: 4.7 moles of SO2
  • Convert to moles of O2:
    • Mole ratio: 2 SO2 : 1 O2
    • Calculation: 4.7 moles SO2 × (1 mole O2 / 2 moles SO2) = 2.35 moles O2

Problem 2: Propane Reaction

• Reaction: C3H8 + O2 → CO2 + H2O

• Balanced Equation: C3H8 + 5 O2 → 3 CO2 + 4 H2O

• Part A: Given: 2.8 moles of C3H8

  • Convert to grams of CO2:
    • M ratio: 1 C3H8 : 3 CO2
    • Molar mass of CO2: 44.01 g/mol
    • Calculation: 2.8 moles C3H8 × (3 moles CO2 / 1 mole C3H8) × 44.01 g/mol = 369.50 g CO2

• Part B: Given: 3.8 moles of C3H8

  • Convert to grams of O2:
    • M ratio: 1 C3H8 : 5 O2
    • Molar mass of O2: 32 g/mol
    • Calculation: 3.8 moles C3H8 × (5 moles O2 / 1 mole C3H8) × 32 g/mol = 608 g O2

• Part C: Given: 25 g of C3H8

  • Convert to moles of H2O:
    • Molar mass of C3H8: 44.094 g/mol
    • Convert grams to moles:
      • Calculation: 25 g C3H8 × (1 mole C3H8 / 44.094 g) × (4 moles H2O / 1 mole C3H8) = 2.27 moles H2O

• Part D: Given: 38 g of H2O

  • Convert to moles of CO2:
    • Molar mass of H2O: 18.016 g/mol
    • Calculation: 38 g H2O × (1 mole H2O / 18.016 g) × (3 moles CO2 / 4 moles H2O) = 1.58 moles CO2

Problem 3: Aluminum Reaction

• Reaction: Al + Cl2 → AlCl3

• Balanced Equation: 2 Al + 3 Cl2 → 2 AlCl3

• Part A: Given: 35 g of Al

  • Convert to grams of AlCl3:
    • Molar mass of Al: 26.98 g/mol
    • Molar mass of AlCl3: 133.33 g/mol
    • Calculation: 35 g Al × (1 mole Al / 26.98 g) × (2 moles AlCl3 / 2 moles Al) × (133.33 g AlCl3 / 1 mole AlCl3) = 172.96 g AlCl3

• Part B: Given: 42.8 g of Al

  • Convert to grams of Cl2:
    • Calculation: 42.8 g Al × (1 mole Al / 26.98 g) × (3 moles Cl2 / 2 moles Al) × (70.9 g Cl2 / 1 mole Cl2) = 168.75 g Cl2

Conclusion

• Understanding stoichiometry is essential for conversions in chemistry.
• Practice with various problems to gain proficiency.