Balancing Chemical Equations Lecture Notes

Introduction

• Focus: Balancing chemical equations
• Goal: Ensure atoms are equal on both sides of the reaction
• Process: Balance carbon atoms, hydrogen atoms, and then oxygen atoms

Combustion Reaction Example: Propane

• Equation: C3H8 + O2 → CO2 + H2O
• Steps:
  1. Balance Carbon Atoms:
     • 3 carbon atoms on the left, so 3 in front of CO2
  2. Balance Hydrogen Atoms:
     • 8 hydrogen atoms in C3H8, so 4 in front of H2O
  3. Balance Oxygen Atoms:
     • Total 10 oxygen atoms needed on the right, 5 in front of O2

Combustion Reaction Example: Butane

• Equation: C4H10 + O2 → CO2 + H2O
• Steps:
  1. Balance Carbon Atoms:
     • 4 carbon atoms, so 4 in front of CO2
  2. Balance Hydrogen Atoms:
     • 10 hydrogen atoms, so 5 in front of H2O
  3. Balance Oxygen Atoms:
     • Calculate total oxygen required, divide by 2 for O2.
     • Multiply entire equation by 2 for whole numbers.

Example: Aluminum and Hydrochloric Acid

• Equation: Al + HCl → AlCl3 + H2
• Steps:
  1. Balance Chlorine Atoms:
     • 6 in front of HCl
  2. Balance Hydrogen Atoms:
     • 3 in front of H2
  3. Balance Aluminum Atoms:
     • 2 in front of Al

Example: Gallium and Copper Bromide

• Equation: Ga + CuBr2 → GaBr3 + Cu
• Steps:
  1. Balance Bromine Atoms:
     • Use the least common multiple, LCM = 6
  2. Balance Copper Atoms:
     • 3 in front of Cu
  3. Balance Gallium Atoms:
     • 2 in front of Ga

Example: Iodine and Fluorine

• Equation: I2 + F2 → IF7
• Steps:
  1. Balance Fluorine Atoms:
     • LCM of 2 and 7 = 14, adjust coefficients accordingly

Example: Sulfur Dioxide and Oxygen

• Equation: SO2 + O2 → SO3
• Steps:
  1. Balance Oxygen Atoms:
     • Use fractions initially, then multiply by 2 for whole numbers

Example: Sodium and Sulfur

• Equation: Na + S8 → Na2S
• Steps:
  1. Balance Sulfur Atoms:
     • 8 in front of Na2S
  2. Balance Sodium Atoms:
     • 16 in front of Na

Double Replacement Reaction Example: Sodium Phosphate and Magnesium Chloride

• Equation: Na3PO4 + MgCl2 → NaCl + Mg3(PO4)2
• Steps:
  1. Treat phosphate as a unit
  2. Adjust sodium, magnesium, and chlorine to balance

Double Replacement Reaction Example: Potassium Sulfate and Aluminum Chloride

• Equation: K2SO4 + AlCl3 → KCl + Al2(SO4)3
• Steps:
  1. Treat sulfate as a unit
  2. Adjust potassium, aluminum, and chlorine to balance

Example: Ammonia and Oxygen

• Equation: NH3 + O2 → NO + H2O
• Steps:
  1. Balance Nitrogen Atoms:
     • Initially balanced
  2. Balance Hydrogen Atoms:
     • Adjust coefficients for even numbers
  3. Balance Oxygen Atoms using fractions, then multiply by 2

Combustion Reaction: Ethanol

• Equation: C2H5OH + O2 → CO2 + H2O
• Steps:
  1. Balance Carbon Atoms:
     • 2 in front of CO2
  2. Balance Hydrogen Atoms:
     • 3 in front of H2O
  3. Balance Oxygen Atoms:
     • Consider oxygen in ethanol

Conclusion

• Practice is key to mastering balancing equations
• Focus on systematic balancing of each element
• Balance challenging reactions using common multiples and whole number coefficients

Final Note

• Thanks for attending the lecture. Practice regularly to improve your skills in balancing chemical equations.