L2 - Half-Reactions

Electrochemical reactions involve a transfer of electrons between species. So far in this module you have learned to identify oxidation, reduction, and agents that bring about the oxidation and reduction of other substances. In the previous lesson you sawhalf-reactions for simple changes to the charge of metals and metal ions. You also used empirical evidence, collected as you completed the investigation “Spontaneity of Redox Reactions,” to confirm the half-reactions you prepared.

You also began using the half-reactions listed on the “Table of Selected Standard Electrode Potentials” on page 7 of the Chemistry Data Booklet. Did you look at some of the other reactions in the table? If so, you may have noticed that many of the half-reactions involve more than one species.

Understanding how substances act alone or in combinations to bring about reactions in a chemical system is an important part of designing chemical systems to achieve a desired function. Chemists and technologists are required to investigate the behaviour of materials to ensure the materials will not undergo unwanted side reactions.

In some situations unexpected side reactions can occur when air, water, or other substances are present in a system. If their presence was not expected, an electrochemical reaction could result in the metal's corrosion, which could lead to metal fatigue and/or to a change in the metal's ability to function as intended.

Consider the following questions as you complete this lesson:

• How can combinations of species act together as oxidizing or reducing agents?
• Can half-reactions be used to predict and explain changes that occur within a chemical system?
• Can the same substance be the oxidizing agent and the reducing agent in an electrochemical process?