Net Ionic Equation — Overview & Examples

We've been studying solutions. We've looked at how to measure solution concentration. Now let's look at some chemical reactions! How do we react two solids? Some chemical reactions do happen between solids. In fact, there's an entire branch of chemistry dedicated to them. It's called solid-state chemistry! But generally, they are slow or non-spontaneous. For example, consider two ionic crystals. Their electrostatic interactions make them very stable. It takes a lot of energy to break an ionic bond. They have large bond energys because they are so strong. They would more readily react if they had unrestricted ions. How do we make the ions available? By putting them in solution!

When we react electrolytes, we can write a new variety of chemical equation. The new equation only uses the reactive ions. We call it a Net Ionic Equation.

What are Net Ionic Equations?

A net ionic equation is a chemical equation for aqueous solutions. It only shows the ions and molecules that take part in the reaction. The reactants are all ions. Often, one or more of the products is a precipitate. Remember, you can determine if something is soluble or insoluble using the solubility rules.

Steps for Writing a Net Ionic Equation

1. Write the balanced chemical equation.

2. Write the equation again with all aqueous compounds written as ions.

3. Cancel anything that is both a reactant and a product. It's like a reaction mechanism. Anything that is on both sides is called a spectator ion. They do not take part in the reaction.

4. Rewrite the equation with the remaining ions and precipitates. The resulting equation is the net ionic equation. It shows you the reactive species and the products.

Writing a Net Ionic Equation Example

Let's look at an example. Let's say we react aqueous sodium chloride and silver nitrate.

1. The balanced chemical equation is $NaCl(aq) + AgNO_{3(aq)}\rightarrow NaNO_{3(aq)} + AgCl_{(s)}$.

2. Write every aqueous species as its component ions. So, the equation becomes $Na^{+} + Cl^{-} + Ag^{+} + NO_{3}^{+} \rightarrow Na^{+} + NO_{3}^{-} + AgCl_{(s)}$.

3. Cancel any ions that are on both sides of the equation. $\cancel{Na^{+}} + Cl^{-} + Ag^{+} +\cancel{ NO_{3}^{-}} \rightarrow \cancel{Na^{+}} + \cancel{NO_{3}^{-}} + AgCl_{(s)}$

4. Write the net ionic equation. $Ag^{+} + Cl^{-} \rightarrow AgCl_{(s)}$

Benefits of Net Ionic Equations

So, what's the point of writing net ionic equations? By canceling the spectator ions, we created a generic equation. Anytime we have silver and chloride, we would expect silver chloride to be the product. Net ionic equations show us a general equation for a broad range of reactions. So, for example, let's say we reacted KCl and AgI. We would still expect the reaction to be $Ag^{+} + Cl^{-} \rightarrow AgCl_{(s)}$.

How do we know that chloride will replace iodide? We can predict reactivity with a periodic table or activity series! Our activity series tells us that chlorine is more reactive. When using the periodic table, we broadly follow the electronegativity trend. So, the halogens are easy. Since chlorine is more electronegative, it replaces iodine.

(Video) How To Write Net Ionic Equations In Chemistry - A Simple Method!

by The Organic Chemistry Tutor

In this video, The Organic Chemistry Tutor explains net ionic equations. He walks you, step-by-step, through two examples. His method is simple and concise. Watching this video will help you master writing net ionic equations.