Overview
This lecture introduces chemical equations, explains the difference between word and symbol equations, and details balancing chemical equations with practical examples.
Chemical Equations and Components
- Chemical equations represent what happens in a chemical reaction.
- Reactants are substances present before the reaction, written on the left side of the equation.
- Products are substances formed in the reaction, written on the right side.
- The arrow in the equation points from reactants to products, indicating the direction of the reaction.
Word vs Symbol Equations
- Word equations describe the reactants and products using their names.
- Symbol equations use chemical formulas (e.g., CH₄ for methane, O₂ for oxygen).
- Some elements exist naturally as molecules (e.g., O₂, Cl ₂, N₂) and must be written this way in equations.
Balancing Chemical Equations
- A balanced equation has an equal number of each type of atom on both sides of the arrow.
- Balancing usually requires trial and error, adjusting coefficients (“big numbers” in front) but never the subscripts (“small numbers” in formulas).
- Subscripts denote the actual chemical species and cannot be changed without altering the substance (e.g., O₂ cannot become O₃).
- Only whole numbers are used when balancing equations.
Example 1: Methane Combustion
- Word equation: Methane + Oxygen → Carbon Dioxide + Water.
- Symbol equation: CH₄ + O₂ → CO₂ + H₂O (unbalanced).
- After balancing: CH₄ + 2O₂ → CO₂ + 2H₂O.
Example 2: Sulfuric Acid & Sodium Hydroxide
- Word equation: Sulfuric Acid + Sodium Hydroxide → Sodium Sulfate + Water.
- Symbol equation: H₂SO₄ + NaOH → Na₂SO₄ + H₂O (unbalanced).
- After balancing: H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O.
Tips for Balancing Equations
- Balance the least common elements first.
- Double-check that the number of each type of atom is equal on both sides once done.
Key Terms & Definitions
- Reactant — Substance present at the start of a reaction.
- Product — Substance formed as a result of a reaction.
- Coefficient — Large number in front of a formula, indicating quantity of molecules.
- Subscript — Small number within a formula, indicating number of atoms in a molecule.
- Balanced Equation — An equation with an equal number of each atom on both sides.
Action Items / Next Steps
- Practice writing and balancing chemical equations.
- Review chemical formulas for common compounds and elements.