This entry was posted on October 13, 2021 by Anne Helmenstine (updated on October 18, 2021)
The net ionic equation, complete ionic equation, and molecular equation are three methods of writing chemical equations for reactions in aqueous solution. These are neutralization and precipitation reactions where electrolytes (salt, acids, bases) dissolve in water and react with one another. Here are the definitions of the three types of ionic equations, examples, and a look at when you use each form.
- The molecular equation is the balanced chemical equation for an ionic reaction.
- The complete ionic equations include all species in an ionic reaction, including spectator ions.
- The net ionic equation only shows the species involved in the chemical reaction.
Molecular Equation
The molecular equation is the balanced equation that shows the reactants and products as neutral chemical species. The state of matter of each substance is in parentheses following each formula, where (s) means solid, (l) means liquid, (g) stands for gas, and (aq) means dissolved in aqueous solution.
For example, the molecular equation for the reaction between silver nitrate (AgNO3) and sodium chloride (NaCl) in water is:
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
This is a good type of equation for giving an overview of a chemical reaction. It is also useful when weak acids or bases or incompletely soluble salts are present because they do not fully dissociate into their ions in water.
- For the molecular equation, write the neutral reactants, products, and direction of the reaction.
- List the states of matter of reactants and products in parentheses following the chemical formulas.
- Balance the chemical reaction.
Complete Ionic Equation
The complete ionic equation shows all of the ions in the solution, regardless of whether they participate in the chemical reaction. In other words, the complete ionic equation includes spectator ions. For example, the complete ionic equation for the reaction between silver nitrate and silver chloride is:
<!-MONUMETRIC Repeatable 2 D:300x250 T:300x250 M:300x250,320x50 START->
<!-MONUMETRIC Repeatable 2 D:300x250 T:300x250 M:300x250,320x50 ENDS->
Ag+(aq) + NO3–(aq) + Na+(aq) + Cl–(aq) → AgCl(s) + Na+(aq) + NO3–(aq)
Like the molecular equation, the complete ionic equation lists reactants, products, and their state of matter. However, it also gives the electrical charge of each chemical species. This gives you an easier time balancing chemical equations for both charge and mass. In more complex reactions, it also shows species that may interfere with a reaction or even participate in side-reactions.
- For the complete ionic equation, list all the molecules and ions found in the reaction container.
- List the state of matter in parentheses following each formula.
- Balance the equation for mass and charge.
Net Ionic Equation
The net ionic equation is the pared-down chemical equation that only shows the species participating the the chemical reaction. The spectator ions cancel out and don’t show up in the equation. Spectator ions are ions occurring on both sides of the reaction arrow. Balance the net ionic equation for both mass and charge and include the state of matter of the reactants and products.
Ag+(aq) + NO3–(aq) + Na+(aq) + Cl–(aq) → AgCl(s) + Na+(aq) + NO3–(aq)
For example, for the reaction between silver nitrate and sodium chloride, the net ionic equation is:
Ag+(aq) + Cl–(aq) → AgCl(s)
The net ionic equation tell you at a glance which ions influence product formation and whether or not there is a solid present.
- For the net ionic equation, start with the complete ionic equation. The net ionic equation is balanced for mass and charge and lists the state of matter of all species.
- Cancel out the spectator ions, which appear on both the reactant and product sides of the reaction arrow.
Example of Molecular, Complete, and Net Ionic Equations
For example, here are the molecular, complete, and net ionic equations for the reaction between copper(II) chloride (CuCl2) and potassium phosphate (K3PO4). From the solubility rules, you know copper chloride and potassium phosphate are soluble in water. Also from the solubility rules, you know potassium chloride (KCl) is soluble, while copper(II) phosphate is insoluble.
Unbalance Equation
CuCl2(aq) + K3PO4(aq) → KCl(aq) + Cu3(PO4)2(s)
Molecular Equation
3CuCl2(aq) + 2K3PO4(aq) → 6KCl(aq) + Cu3(PO4)2(s)
Complete Ionic Equation
3Cu2+(aq) + 6Cl−(aq) + 6K+(aq) + 2PO43−(aq) → 6K+(aq) + 6Cl−(aq) + Cu3(PO4)2(s)
Net Ionic Equation
3Cu2+(aq)+2PO43−(aq)→Cu3(PO4)2(s)
References
- Atkins P.; de Paula, J. (2006).Physical Chemistry(8th ed.). W.H. Freeman. ISBN 978-0-7167-8759-4.
- Brady, James E.; Senese, Frederick; Jespersen, Neil D. (2007). Chemistry: Matter and Its Changes. John Wiley & Sons. ISBN 9780470120941.
- Laidler, K. J. (1978).Physical Chemistry with Biological Applications. Benjamin/Cummings. ISBN 978-0-8053-5680-9.
- Petrucci, Ralph H.; Harwood, William S.; Herring, F. Geoffrey (2002).General Chemistry: Principles and Modern Applications(8th ed.). Upper Saddle River, N.J: Prentice Hall. ISBN 978-0-13-014329-7.
- Zumdahl, Steven S. (1997).Chemistry(4th ed.). Boston, MA: Houghton Mifflin Company. ISBN 9780669417944.
