Writing Balanced Chemical Equations

1. Writing Balanced Chemical Equations

2. Law of Conservation of Mass • In normal chemical processes (non-nuclear) mass can be neither created nor destroyed. • Application: • The numbers and types of atoms must be exactly the same on both sides of the chemical equation. • massbefore rxn = massafter rxn

3. Step 1 • Determine formulas of all reactants and products using the rules of nomenclature and their required oxidation states.

4. Step 2 • Classify the Reaction as… • Single displacement • Double displacement • Combustion • Synthesis • Decomposition

5. Step 3 • Use proper notation to write an unbalanced equation. • Reactants to the left • Products to the right • Reactants → Products • Symbols: • → yields • (s) solid • (l) liquid • (g) gas • (aq) aqueous – means water solution • (cr) crystalline • Up or down arrows to indicate gas evolved or precipitate • (g)  or (s) ↓ • Indicate special conditions above the yields sign • Acid, base, catalysts, heat, temperature, acidic, basic

6. Step 4 • Balance using the following rules • Do not change subscripts after you have determined proper formulas • Change only coefficients • Do not insert coefficients within a chemical formula • Reduce coefficients to lowest terms

7. Rules of Thumb • Balance free elements last • Balance oxygen last • Focus on only one element at a time • Balance polyatomic ions as a unit if possible • Use fractional coefficients if helpful, but remember to multiply the entire equation by 2 to get rid of the fractions