Redox Overview fall 2009

Redox Overview fall 2009 - 1 Electrochemistry Oxidation and...

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1 Electrochemistry – Oxidation and Reduction Reactions Oxidation-Reduction Reactions In our previous studies, we examined reactions that occurred in aqueous solutions that involved formation of water (acid-base neutralization) and formation of a solid (precipitation) as the driving force of the chemical reactions. During these reactions, all substances maintained their charge after the reactions were completed. Another type of reaction, which occurs in both aqueous solutions and in reactions where substances are burned in the presence of oxygen gas, involves a transfer of electrons as the driving force of the chemical reaction. The reactants in these reactions will lose or gain electrons and change their charge as they form the products. The driving force of these chemical changes is electron transfer and they are called oxidation and reduction reactions. Oxidation-reduction reactions are a very important class of chemical reactions. They occur all around us and even within us. The bulk of the energy needed for the functioning of all living organisms, including humans, is obtained from food through oxidation-reduction processes. Such diverse phenomena as the electricity obtained from a battery to start a car, the use of natural gas to heat a home, iron rusting, and the functioning of antiseptic agents to kill or prevent the growth of bacteria all involve oxidation-reduction reactions. The knowledge of this type of reaction is fundamental to understanding many biological and technological processes. Historically, the word oxidation was first used to describe the reaction of a substance with oxygen. According to this historical definition, each of the following reactions involves oxidation: 4 Fe (s) + 3 O 2 (g) Æ 2 Fe 2 O 3 (s) S (s) + O 2 (g) Æ SO 2 (g) CH 4 ( g) + 2 O 2 (g) Æ CO 2 (g) + 2 H 2 O (g) Originally, the term reduction referred to processes where oxygen was removed from a compound. A particularly common type of reduction reaction, according to the original definition, is the removal of oxygen from a metal oxide to produce free metal. CuO (s) + H 2 (g) Æ Cu (s) + H 2 O (g) 2 Fe 2 O 3 (s) + 3 C (s) Æ 4 Fe (s) + 3 CO 2 (g) Today the words oxidation and reduction are used in a much broader sense. Current definitions include the previous examples but also include reactions with numerous non-oxygen containing substances. Reactions that involve the transfer of electrons from one reactant to another reactant, regardless of the substances involve, are collectively called oxidation-reduction reactions (redox). The reactants in these reactions will lose or gain electrons and change their charge as they form the products. Oxidation is the process in which a substance in a chemical reaction loses electrons. Reduction is the process in which a substance in a chemical reaction gains electrons.
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Redox Overview fall 2009 - 1 Electrochemistry Oxidation and...

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