Stoichiometry Basics and Problem-Solving

Key Concepts

• Stoichiometry deals with the calculation of reactants and products in chemical reactions.
• There are three main types of stoichiometric conversions:
  1. Moles of Substance A to Moles of Substance B
  2. Moles of Substance A to Grams of Substance B (or vice versa)
  3. Grams of Substance A to Grams of Substance B

Conversion Types

1. Moles to Moles Conversion

   • Example Problem 1: Sulfur dioxide reacts with oxygen to form sulfur trioxide.
     • Equation: 2SO₂ + O₂ → 2SO₃
     • Given: 3.4 moles of SO₂
     • Solution: Use molar ratio (2:2) to find moles of SO₃. Result: 3.4 moles of SO₃ because the molar ratio is 1:1.
   • Example Problem 2: Determine how many moles of O₂ react with 4.7 moles of SO₂.
     • Solution: Use molar ratio (2:1). Result: 2.35 moles of O₂.

2. Moles to Grams Conversion

   • Example Problem 3: Propane (C₃H₈) reacts with O₂ to form CO₂ and H₂O.
     • Equation: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
     • Given: 2.8 moles of C₃H₈
     • Solution:
       • Convert moles of C₃H₈ to moles of CO₂ using molar ratio (1:3).
       • Convert moles of CO₂ to grams using molar mass (44.01 g/mol).
       • Result: 369.50 grams of CO₂.
   • Example Problem 4: Find grams of O₂ reacting with 3.8 moles of C₃H₈.
     • Solution: Use molar ratio (1:5) and molar mass of O₂ (32 g/mol). Result: 608 grams of O₂.

3. Grams to Moles to Grams Conversion

   • Example Problem 5: Given 25g C₃H₈, find moles of H₂O produced.
     • Solution:
       • Convert grams to moles using molar mass of C₃H₈ (44.09 g/mol).
       • Use ratio (1:4) to find moles of H₂O.
       • Result: 2.27 moles of H₂O.
   • Example Problem 6: Given 38g H₂O, find moles of CO₂ produced.
     • Solution:
       • Convert grams to moles using molar mass of H₂O (18.016 g/mol).
       • Use ratio (3:4) to find moles of CO₂.
       • Result: 1.58 moles of CO₂.

Aluminum and Chlorine Reaction

• Equation: 2Al + 3Cl₂ → 2AlCl₃

1. Grams to Grams Conversion
   • Example Problem 7: Convert 35g of Al to grams of AlCl₃.
     • Solution:
       • Convert grams of Al to moles.
       • Use molar ratio (2:2) and molar mass of AlCl₃ (133.33 g/mol) to find grams.
       • Result: 172.96g of AlCl₃.
   • Example Problem 8: Convert 42.8g of Al to grams of Cl₂.
     • Solution:
       • Convert grams of Al to moles.
       • Use molar ratio (2:3) and molar mass of Cl₂ (70.9 g/mol) to find grams.
       • Result: 168.75g of Cl₂.

Conclusion

• Stoichiometry involves understanding and applying molar ratios and molar masses to convert between moles and grams.
• Common conversions include mole-to-mole, mole-to-gram, and gram-to-gram.