Overview
This lecture introduces balancing chemical equations, explains the difference between balanced and unbalanced equations, and demonstrates the steps and rules for balancing equations using examples.
What is a Chemical Equation?
- A chemical equation represents a chemical reaction using formulas for reactants and products.
- A word equation uses words to describe the reactants and products; a chemical equation uses chemical symbols and formulas.
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 one or more types of atoms on the two sides of the arrow.
Steps to Balance a Chemical Equation
- Count the number of each type of atom on both sides of the equation.
- Adjust the number of molecules (coefficients) to achieve the same number of each atom on both sides.
- Only change coefficients in front of compounds; never change the subscripts within formulas.
Examples of Balancing Equations
- For the reaction H₂ + Cl₂ → HCl:
- Unbalanced: 2 H and 2 Cl on left, 1 H and 1 Cl on right.
- Balanced: H₂ + Cl₂ → 2 HCl.
- For the reaction H₂ + O₂ → H₂O:
- Unbalanced: 2 H, 2 O on left; 2 H, 1 O on right.
- Balanced: 2 H₂ + O₂ → 2 H₂O.
- For the reaction N₂ + H₂ → NH₃:
- Use a chart to track number of atoms.
- Balanced: N₂ + 3 H₂ → 2 NH₃.
Common Mistakes & Rules
- Do not change subscripts in chemical formulas while balancing.
- Changing subscripts creates new compounds with different properties.
- Only add coefficients in front of compounds to balance atoms.
Using Tools to Balance Equations
- Visual diagrams help understand atom balancing, but use charts/maths for homework and tests.
- Practice balancing with charts that list the count of each atom on both sides.
Key Terms & Definitions
- Chemical equation — a symbolic representation of a chemical reaction.
- Balanced equation — an equation with equal numbers of each atom on both sides.
- Unbalanced equation — an equation with unequal numbers of atoms.
- Coefficient — a number placed in front of a molecule to indicate quantity.
- Subscript — a small number in a chemical formula showing the number of atoms in a molecule.
Action Items / Next Steps
- Practice balancing chemical equations using provided or additional example problems.
- Watch the recommended video on balancing chemical equations practice problems.