Introduction to Stoichiometry

Types of Conversions in Chemical Reactions

1. Moles of Substance A to Moles of Substance B
   • Identify the molar ratio.
   • Single-step conversion.
2. Moles of Substance A to Grams of Substance B (or vice versa)
   • Two-step process: Convert moles to moles, then moles to grams.
3. Grams of Substance A to Grams of Substance B
   • Three-step process: Convert grams to moles, change substance, convert moles to grams.

Example Problems

Example 1: Sulfur Dioxide and Oxygen

• Reaction: Sulfur dioxide reacts with oxygen to form sulfur trioxide.
• Balanced Equation:
  • SO2 + O2 → SO3
  • Balanced: 2 SO2 + O2 → 2 SO3
• Problem 1: Convert moles of SO2 to moles of SO3
  • Given: 3.4 moles of SO2
  • Molar ratio SO2 to SO3 is 2:2
  • Answer: 3.4 moles of SO3
• Problem 2: Convert moles of SO2 to moles of O2
  • Given: 4.7 moles of SO2
  • Molar ratio SO2 to O2 is 2:1
  • Answer: 2.35 moles of O2

Example 2: Propane and Oxygen

• Reaction: Propane reacts with oxygen to form carbon dioxide and water.
• Balanced Equation:
  • C3H8 + 5 O2 → 3 CO2 + 4 H2O
• Problem 1: Convert moles of propane to grams of CO2
  • Given: 2.8 moles of C3H8
  • Molar ratio C3H8 to CO2 is 1:3
  • Molar mass CO2 = 44.01 g/mol
  • Answer: 369.50 grams of CO2
• Problem 2: Convert moles of propane to grams of O2
  • Given: 3.8 moles of C3H8
  • Molar ratio C3H8 to O2 is 1:5
  • Molar mass O2 = 32 g/mol
  • Answer: 608 grams of O2
• Problem 3: Convert grams of C3H8 to moles of H2O
  • Given: 25 grams of C3H8
  • Molar mass C3H8 = 44.094 g/mol
  • Molar ratio C3H8 to H2O is 1:4
  • Answer: 2.27 moles of H2O
• Problem 4: Convert grams of H2O to moles of CO2
  • Given: 38 grams of H2O
  • Molar mass H2O = 18.016 g/mol
  • Molar ratio H2O to CO2 is 4:3
  • Answer: 1.58 moles of CO2

Example 3: Aluminum and Chlorine

• Reaction: Aluminum reacts with chlorine gas to form aluminum chloride.
• Balanced Equation:
  • 2 Al + 3 Cl2 → 2 AlCl3
• Problem 1: Convert grams of Al to grams of AlCl3
  • Given: 35 grams of Al
  • Molar mass Al = 26.98 g/mol
  • Molar mass AlCl3 = 133.33 g/mol
  • Answer: 172.96 grams of AlCl3
• Problem 2: Convert grams of Al to grams of Cl2
  • Given: 42.8 grams of Al
  • Molar mass Cl2 = 70.9 g/mol
  • Molar ratio Al to Cl2 is 2:3
  • Answer: 168.75 grams of Cl2

Conclusion

• Understanding stoichiometry involves performing various conversions between moles and grams.
• Key stoichiometry problems include mol-to-mol, mol-to-gram, gram-to-mol, and gram-to-gram conversions.