A molecular equation is represented by a balanced chemical equation where the reactants and products are written in their neutral forms. By eliminating its spectator ions the molecular equation is transformed into the net ionic equation.
How to determine the Net Ionic Equation
A molecular equation can only result if you produce a solid, liquid or gas as a product. To determine if these states of matter are formed you use the solubility rules and your understanding of weak and strong electrolytes.
Take for instance the acid-base reaction between hydrochloric acid, HCl, and sodium hydroxide, NaOH.
STEP 1: Write the molecular equation and determine the phases of your products.
In this example the chemical reaction occurs because a liquid was formed. Chemical reactions that produce a solid as a product are termed precipitation reactions.
STEP 2: Based on your understanding of soluble ionic compounds and electrolytes we must give the total or complete ionic equation. Keep in mind that if the coefficients of the compounds were different they would change the number of each ion produced.
In this step we break up only the soluble aqueous compounds into ions, while solids, liquids and gases stay intact.
STEP 3: The spectator ions represent the ions that remain unchanged in a chemical reaction. They look the same on both sides of the chemical equation.
The spectator ions represent the ions that haven’t reacted and remain suspended and dissolved in the solution.
Eliminating the spectator ions gives the net ionic equation.