Lecture Notes: Chemical Reactions and Balancing Equations

Introduction

• Presenter: Dr. Michelle Banogan
• Topic: Chemical Reactions
• Focus: Writing and balancing chemical equations
• Previous Knowledge: Atoms and molecules

Learning Goals

• Derive chemical equations from narrative descriptions
• Write and balance chemical equations in molecular format

Key Concepts

Chemical Equations

• Components of Equations:
  • Reactants: Substances undergoing reaction (left side)
  • Products: Substances formed (right side)
  • Coefficients: Numbers in front of chemical species indicating quantity
  • Symbols: Represent molecules and atoms (e.g., CH₄ for methane, O₂ for oxygen)

Example Reaction

• Reaction: CH₄ + 2O₂ → CO₂ + 2H₂O
  • Reactants: Methane (CH₄) and Oxygen (O₂)
  • Products: Carbon Dioxide (CO₂) and Water (H₂O)
  • Coefficients: Indicate the number of molecules

Vocabulary

• Reactants and Products: Separated by plus signs and an arrow
• Coefficients: Represent the relative numbers of reactants and products
  • Use the smallest possible whole number coefficients
  • Coefficients can be interpreted as ratios

Balancing Chemical Equations

Importance of Balancing

• Requires equal numbers of atoms for each element on both sides of the equation
• Calculated by multiplying coefficients

Example: Methane Combustion

• Carbon Atoms:
  • Reactant Side: 1 carbon
  • Product Side: 1 carbon
  • Balanced
• Hydrogen Atoms:
  • Reactant Side: 4 hydrogens
  • Product Side: 4 hydrogens
  • Balanced
• Oxygen Atoms:
  • Reactant Side: 4 oxygens (2 x 2)
  • Product Side: 4 oxygens (2 in CO₂ + 2 in H₂O)
  • Balanced

Balancing Strategy

1. Inspect Initial Balances: Evaluate numbers on both sides
2. Adjust Coefficients: Only coefficients can be changed, not subscripts
3. Use Ratios and Multiples: Achieve balance by manipulating coefficients

Example Problems

1. Water into Elements: H₂O → H₂ + O₂

   • Initial Balance: Hydrogens balanced, Oxygens not
   • Solution: Adjust water molecules to 2H₂O → 2H₂ + O₂

2. Nitrogen and Oxygen Reaction: N₂ + O₂ → N₂O₅

   • Initial Balance: Not balanced
   • Solution: Adjust using LCM for oxygen, resulting in 2N₂ + 5O₂ → 2N₂O₅

Using Fractions in Balancing

• Sometimes use fractions to balance, later convert to integer coefficients
• Example: C₂H₆ + O₂ → CO₂ + H₂O, initially balanced using fractions
• Final Solution: Multiply through by common denominator to achieve integer coefficients

Conclusion

• Balancing equations involves ensuring equal numbers of each type of atom
• Skills in balancing are critical for understanding chemical reactions