Chemistry Definitions: What Is a Molecular Equation?

A molecular equation is a balanced chemical equation in which the ionic compounds are expressed as molecules rather than component ions.

The Simplest Molecular Equation

The molecular formula of a compound lists all its component elements and the number of atoms each element contains. The simplest formula is similar: all the elements are listed, but the numbers correspond to the ratios between the elements. 

KNOMolecular vs. Ionic Equations

For a reaction involving ionic compounds, there are three types of equations that can be written: molecular equations, complete ionic equations, and net ionic equations. All of these equations have their place in chemistry. A molecular equation is valuable because it shows exactly what substances were used in a reaction. A complete ionic equation shows all the ions in a solution, while a net ionic equation shows only the ions that participate in a reaction to form products.

For example, in the reaction between sodium chloride (NaCl) and silver nitrate (AgNO₃), the molecular equation is:

NaCl(aq) + AgNOThe complete ionic equation is:

NaThe net ionic equation is written by canceling out the species that appear on both sides of the complete ionic equation and thus don't contribute to the reaction. For this example, the net ionic equation is:

Ag