Imagine that you took to two colourless solutions and mixed them together in the hope of observing a spectacular chemical reaction. If after mixing the two solutions together, the resulting solution was still colourless, could you say that you have just witnessed a chemical reaction?
Since there is no evidence of a chemical change you can not say that you have just witnessed a chemical reaction. If a reaction is taking place in solution (the reactants are dissolved in water) then we can only say that a product has formed and a chemical reaction has taken place if the product has come out of the solution. We will know the product has come out of the solution if it is a solid, liquid, or gas rather than a substance that remains dissolved in water.
Here’s another illustration to consider. Imagine you in sitting in the stands at a hockey game watching your favourite team play. When your favourite team wins the game, did you in participate in winning that game? Now, if we forget about the role a crowd plays in the positive momentum of the game then we can say that no, you did not physically participate in winning the game. You were simply a spectator at the game. It was only the players on the winning team that actually won the game.
Many reactions take place in a aqueous environment. An aqueous environment is a solution where water is the solvent. Generally, an aqueous solution will consist of ions that are dissolved in water. If we consider the aqueous environment to be like the hockey arena, then who are the spectators and who is the winning team? The spectators in a reaction that takes place in an aqueous environment are the ions that do not participate in forming the product. The ions that actually form the product we can then consider to be like the winning team.
Let’s take a look at an example of a reaction that involves spectator ions and learn how to write the net ionic equation for a chemical reaction. A net ionic equation omits the spectator ions in a chemical equation and only includes the ions that actually form the product. Remember that the product will by a solid, liquid or gas and not aqueous.