Overview
This lecture covers how to represent and balance chemical reactions using word and symbol equations, including the key steps and rules for balancing.
Chemical Equations
- Chemical reactions can be shown as word equations (using names) or symbol equations (using chemical formulas).
- Reactants are substances present before the reaction; products are substances formed after the reaction.
- The arrow in the equation means reactants are converted into products.
Writing Symbol Equations
- Symbol equations use chemical formulas, e.g., CH₄ + O₂ → CO₂ + H₂O for methane burning in oxygen.
- Some elements exist as molecules (e.g., O₂, Cl₂, N₂) and must be written that way in equations.
Balancing Chemical Equations
- A balanced equation has the same number of each type of atom on both sides of the arrow.
- Use only whole numbers in front of substances to balance equations; do not change subscript numbers in formulas.
- Only adjust the coefficients (big numbers in front), not the subscripts (small numbers in formulas).
- Balancing often requires trial and error.
Example: Methane Combustion
- Unbalanced: CH₄ + O₂ → CO₂ + H₂O.
- Balanced: CH₄ + 2O₂ → CO₂ + 2H₂O.
- Must use O₂ and adjust coefficients to ensure equal atoms on both sides.
Example: Sulfuric Acid and Sodium Hydroxide
- Unbalanced: H₂SO₄ + NaOH → Na₂SO₄ + H₂O.
- Balanced: H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O.
- Balance less common elements first, then adjust others as needed.
Key Terms & Definitions
- Reactant — Substance present at the start of a reaction.
- Product — Substance produced by a reaction.
- Word Equation — Describes a reaction using names of substances.
- Symbol Equation — Uses chemical formulas to represent a reaction.
- Coefficient — Large number in front of a chemical formula indicating quantity.
- Subscript — Small number within a formula indicating number of atoms in a molecule.
- Balanced Equation — Equation with equal atoms of each element on both sides.
Action Items / Next Steps
- Practice balancing chemical equations using both word and symbol forms.
- Review definitions of key terms, especially reactants and products.