Overview
This lecture explains how to represent and balance chemical reactions using word and symbol equations, providing step-by-step guidance with examples.
Chemical Equations and Word Equations
- Chemical reactions can be shown using word equations or symbol equations.
- Reactants (left side) are substances that react, products (right side) are substances formed.
- An arrow indicates the direction of the reaction (reactants form products).
Symbol Equations and Formulas
- Symbol equations use chemical symbols (e.g., CH₄ for methane, O₂ for oxygen).
- Elements like oxygen, nitrogen, and chlorine exist as diatomic molecules (O₂, N₂, Cl₂).
Balancing Chemical Equations
- A balanced chemical equation has the same number of each atom on both sides.
- Only change the big numbers (coefficients) in front of compounds/elements, not the small numbers (subscripts) within formulas.
- Coefficients represent the number of molecules; subscripts are part of the chemical identity.
- Use only whole numbers in balancing equations.
- Balancing often requires trial and error.
Example: Balancing Combustion of Methane
- The unbalanced equation: CH₄ + O₂ → CO₂ + H₂O.
- To balance, adjust coefficients: 1 CH₄ + 2 O₂ → 1 CO₂ + 2 H₂O.
Example: Balancing Sulfuric Acid with Sodium Hydroxide
- The unbalanced equation: H₂SO₄ + NaOH → Na₂SO₄ + H₂O.
- Balance sodium by adding a 2 in front of NaOH: H₂SO₄ + 2 NaOH → Na₂SO₄ + H₂O.
- Balance water by changing coefficient: H₂SO₄ + 2 NaOH → Na₂SO₄ + 2 H₂O.
Key Terms & Definitions
- Reactants — substances that start a chemical reaction (left side).
- Products — substances formed by a chemical reaction (right side).
- Symbol Equation — a chemical equation using symbols and formulas.
- Balanced Equation — an equation with equal numbers of each atom type on both sides.
- Coefficient — large number in front of a formula, indicating quantity.
- Subscript — small number in a formula, indicating number of atoms in a molecule.
- Diatomic Molecule — a molecule made of two atoms (e.g., O₂).
Action Items / Next Steps
- Practice balancing additional chemical equations for homework.
- Review the definitions of key terms.