Oxidation-Reduction

12

These skills are usually tested on the SAT Subject Test in Chemistry. You
should be able to...

Assign oxidation states to elements in compounds.

Describe the process of oxidation and reduction.

Recognize when a substance is being oxidized or reduced.

Apply the appropriate terms to substances involved in redox

reactions.

Use the concepts of oxidation-reduction to better describe

combustion reactions.

This chapter will review and strengthen these skills. Be sure to do the
Practice Exercises at the end of the chapter.

In Chapter 8, the reaction category called single replacement was discussed.

Recall that this type of reaction is characterized by a compound reacting with an
element producing a new compound and a new element. It was shown that
reactions such as these could be predicted to occur (i.e., be spontaneous) if the
heat of formation of the compound in the products is negative and reasonably
bigger than that of the compound in the reactants. These situations produce
exothermic reactions, those in which the system under study becomes lower in
energy, which nature tends to want to see occur.
Delving deeper into single replacement reactions allows one to understand
why the energy of the system goes down in terms of the chemical process that is
occurring. Take the reaction between a solution of silver nitrate and copper metal.

2 AgNO 3 (aq) + Cu(s) → Cu(NO 3 ) 2 (aq) + 2 Ag(s)

The solution of silver nitrate is actually composed of silver ions (Ag+) and

nitrate ions (NO 3 −) surrounded by water molecules in solution. Likewise, the

solution of copper(II) nitrate in the products contains ions of Cu2+ and NO 3 −. The

nitrate ions, then, are found in both the reactants and the products. As discussed in
Chapter 4, they can be referred to as spectator ions. Because spectator ions can