4. Balancing Equations: Writing Word & Symbol Equations
1. Chemical Equations
Chemical equations show what happens during a chemical reaction. They consist of:
Reactants: The substances you start with (written on the left side).
Products: The new substances produced by the reaction (written on the right side).
The Arrow: A single arrow in the middle shows that the reactants react completely to form the products.
2. Word vs. Symbol Equations
Word Equations: Use the full names of the chemicals.
Example: methane + oxygen → carbon dioxide + water
Symbol Equations: Use chemical symbols (e.g., CH₄ + O₂ → CO₂ + H₂O).
Diatomic Molecules: Certain elements always exist as pairs of atoms when they are alone. You must write them as O₂ (oxygen), Cl₂ (chlorine), or N₂ (nitrogen) in equations.
3. The Rules of Balancing
An equation is balanced when there is the same number of each type of atom on both sides of the arrow.
Rule 1: Never change the small numbers (subscripts). Changing a small number changes the actual chemical. For example, changing O₂ to O₃ turns oxygen into ozone.
Rule 2: Change the big numbers (coefficients) in front. A big number tells you how many molecules of that substance you have (e.g., 2 H₂O means two water molecules).
Rule 3: Use whole numbers. Do not use fractions like 1/2.
Process: Balancing is often a process of trial and error. Keep adjusting the big numbers until the counts for every element match on both sides.
4. Example: Balancing Methane Combustion
Unbalanced: CH₄ + O₂ → CO₂ + H₂O
Left: 1 Carbon, 4 Hydrogen, 2 Oxygen
Right: 1 Carbon, 2 Hydrogen, 3 Oxygen
Balanced: CH₄ + 2O₂ → CO₂ + 2H₂O
Adding a "2" in front of O₂ and a "2" in front of H₂O gives 4 Hydrogen and 4 Oxygen atoms on both sides.
5. Balancing Strategy
Start with the least common elements: It is often easier to balance elements like sulfur or sodium before moving on to oxygen or hydrogen.
Double Check: Always perform a final count of every atom on both sides to ensure the numbers are exactly equal.