Overview
The lecture explains how to balance chemical equations using a five-step approach, emphasizing counting atoms, using coefficients, and recognizing polyatomic ions.
Steps to Balance Chemical Equations
- Step 1: Count each type of atom on both sides of the equation.
- If there is no subscript or coefficient, assume it is "1".
- Only change the coefficients (numbers in front of molecules) to balance atoms, never the subscripts.
- Adjust coefficients to equalize the number of each atom on both sides.
- Check your work to confirm the number of atoms matches for every element.
Example Problems
- To balance S₈ + O₂ → SO₂: Change SO₂ coefficient to 8 and O₂ coefficient to 8 for all atoms to balance.
- For H₂ + O₂ → H₂O: Place 2 as the coefficient for H₂O and for H₂, resulting in balanced hydrogen and oxygen.
- For equations with polyatomic ions (e.g., SO₄ or NO₃ present on both sides), treat the ion as a single unit to simplify balancing.
- For equations like CH₄ + O₂ → CO₂ + H₂O, count all atoms carefully, adjust hydrogen and oxygen coefficients, and check totals at the end.
Tips and Reminders
- Only coefficients may be changed when balancing equations.
- Sometimes polyatomic ions remain unchanged on both sides and can be balanced as single units.
- Always count all atoms, including those within compound formulas.
- Practice is necessary to increase speed and accuracy.
Key Terms & Definitions
- Coefficient — A number placed in front of a compound or element to indicate how many units are present.
- Subscript — A small number after an element symbol showing how many atoms of that element are in the molecule.
- Polyatomic Ion — A charged ion composed of two or more atoms bonded together.
Action Items / Next Steps
- Practice balancing chemical equations to improve proficiency.
- Review notes on counting atoms and identifying polyatomic ions.