Law of Conservation of Mass: This principle dictates that the total mass of the reactants must equal the total mass of the products because atoms are simply rearranged, not destroyed.
Electrical Neutrality: In ionic compounds, the sum of positive charges from metal ions must exactly equal the sum of negative charges from non-metal or polyatomic ions.
Fixed Formulae: The chemical formula of a substance (e.g., ) is determined by chemical bonding and cannot be altered to balance an equation; only the coefficients in front of the formula can change.
Step 1: Write the Skeleton Equation: List the correct chemical formulas for all reactants on the left and products on the right.
Step 2: Inventory Atoms: Count the number of atoms for each element present on both sides of the equation.
Step 3: Apply Coefficients: Place whole numbers (coefficients) in front of formulas to equalize atom counts, starting with the most complex molecule.
Step 4: Combustion Priority: When balancing organic combustion, follow the specific order of balancing Carbon first, then Hydrogen, and finally Oxygen.
Step 5: Add State Symbols: Indicate the physical state of each substance using for solid, for liquid, for gas, and for aqueous solution.
Dissociation: When ionic compounds dissolve in water (), they separate into their constituent ions, which move independently in the solution.
Spectator Ions: These are ions that appear on both the reactant and product sides of a chemical equation but do not participate in the actual chemical change.
Net Ionic Equations: A simplified equation that removes spectator ions to show only the species that undergo a chemical change, such as the formation of a precipitate or water.
| Feature | Molecular Equation | Net Ionic Equation |
|---|---|---|
| Scope | Shows all neutral compounds | Shows only reacting species |
| Detail | Includes spectator ions | Excludes spectator ions |
| Usage | General reaction overview | Highlighting the chemical change |
The 'Check-Back' Rule: Always perform a final count of every atom on both sides after you think the equation is balanced; one small error can invalidate the entire stoichiometry.
Polyatomic Brackets: When balancing compounds with polyatomic ions like , treat the ion as a single unit if it appears unchanged on both sides to simplify the process.
Charge Balance: In ionic equations, ensure the net charge on the left side equals the net charge on the right side; they don't have to be zero, but they must be equal.
State Symbol Precision: Pay close attention to the environment of the reaction; for example, water is at room temperature but in high-temperature combustion.
