Chapter 7 · Chemical Reactions
7.7Writing Chemical Equations for Reactions in Solution
12 min · two checks
Predict
Which ions are spectators when AgNO₃(aq) reacts with NaCl(aq)?
The idea
- Write molecular, complete ionic, and net ionic equations.
- Identify spectator ions.
The molecular equation writes full formulas: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq). The complete ionic equation splits each soluble ionic compound into ions and leaves the solid together: Ag⁺ + NO₃⁻ + Na⁺ + Cl⁻ → AgCl(s) + Na⁺ + NO₃⁻. Spectator ions show up unchanged on both sides. Cancel them and the net ionic equation remains: Ag⁺(aq) + Cl⁻(aq) → AgCl(s).
Do not split solids, liquids, or gases. Do not split weak acids or most molecular compounds; you will treat strong acids as fully split when you meet them. If everything cancels, there was no net reaction. Coefficients in the net equation should be the smallest integers. Charges must balance as well as atoms.
Keep these
- Molecular: full formulas. Complete ionic: soluble salts split.
- Spectators cancel. What remains is the net ionic equation.
- Keep (s), (l), and (g) together.
Worked path
Write the net ionic equation for Pb(NO₃)₂(aq) + 2 KI(aq) → PbI₂(s) + 2 KNO₃(aq).
Observe
Soluble: lead nitrate, potassium iodide, potassium nitrate. Insoluble: PbI₂.