Overview
This lecture introduces balancing chemical equations, explains the difference between balanced and unbalanced equations, and demonstrates methods to achieve balance using examples and basic rules.
Balanced vs. Unbalanced Equations
- A balanced equation has the same number of each type of atom on both sides of the arrow.
- An unbalanced equation has different numbers of at least one type of atom on either side.
- Chemical equations must be balanced before being used for calculations or problem-solving.
Process of Balancing Equations
- Write chemical formulas for all reactants and products (e.g., H₂ + Cl₂ → HCl).
- Count the number of each atom type on both sides of the equation.
- Adjust the number of molecules (using coefficients in front) to balance atoms on both sides.
- Example: H₂ + Cl₂ → 2HCl balances two hydrogens and two chlorines on each side.
Examples of Balancing
- For H₂ + O₂ → H₂O:
- Count atoms: Left side has 2 H, 2 O; right side has 2 H, 1 O.
- Add another H₂O molecule: H₂ + O₂ → 2H₂O.
- Adjust H₂: 2H₂ + O₂ → 2H₂O (now 4 H, 2 O on both sides).
- Never change the subscripts (the little numbers in formulas) to balance equations.
Rules and Common Mistakes
- Only change coefficients (numbers in front) when balancing, never the subscripts in a formula.
- Changing subscripts changes the substance itself (e.g., H₂O becomes H₂O₂, which is not water).
Balancing Using Charts
- Create a chart to count each type of atom on both sides.
- Adjust coefficients step by step to balance the atoms.
- Example: For N₂ + H₂ → NH₃, use a chart to find that N₂ + 3H₂ → 2NH₃ balances both N and H.
Key Terms & Definitions
- Balanced Equation — a chemical equation with equal numbers of each atom type on both sides.
- Unbalanced Equation — a chemical equation with unequal numbers of one or more atom types.
- Coefficient — the number placed in front of a chemical formula to indicate the quantity of molecules.
- Subscript — a small number written to the lower right in a formula, indicating the number of atoms in a molecule.
Action Items / Next Steps
- Practice balancing chemical equations using the described methods and charts.
- Watch practice problem videos or complete assigned exercises on balancing equations.