Module 4.2 - Common Reaction Types

Exchange Reactions

Exchange reactions are those in which cations and anions that were partners in the reactants are interchanged in the products.

In exchange reactions, the products must remain electrically neutral. It is this fact that allows you to easily predict the products of these reactions. Let's work through an example to see how this works:

Hydrochloric acid (HCl) can be used to dissolve rust (Fe₂O₃). The reaction that occurs is an exchange reaction. In order to predict the products of this reaction, we must first look at the oxidation number (or charge) of each atom in the reactants.

Both Fe₂O₃ and aqueous HCl are made up of ions. Using the equation below, first click on the positive ions in each reactant. Then fill in the actual charges of the ions in the table below.

	Fe		H			Click here to review ion charges
	O		Cl

Now that you have correctly identified the cations and anions and their respective charges, it is easy to predict the product of the reaction. Since this is an exchange reaction, the cation from the first reactant will combine with the anion from the second reactant while the anion from the first reactant will combine with the cation from the second reactant:

How many hydrogen ions are needed to balance the -2 charge of the oxygen? How many chlorine ions are needed to balance the +3 charge of the iron?

HO
FeCl

Now that you have predicted the products for the reaction, all that is left is to balance the overall equation.

Fill in the appropriate stoichiometric coefficients below to balance this exchange reaction.

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