The Chemical Reaction, Part 3 - Redox Chemical Systems, An Introduction

Greetings,

This post will introduce the concept of oxidation-reduction reactions and some of the many places we can find them.

Oxidation States and Their Determination

An oxidation-reduction (aka., red-ox or just redox) reaction involves a transfer of electrons from one chemical species to another.  This chemical species can be an element or a compound.  A term called Oxidation-State is used to indicate the number of electrons which may be transferred (lost or gained) by a particular atom or ion contained within the chemical species.  If the chemical species is a binary ionic compound, then the oxidation states are numerically equal to the electrical charges of the monoatomic ions contained therein.  Ternary ionic compounds often contain polyatomic oxyions.  The central element of most oxyions are capable of two or more oxidation states.  The sum of the oxyion oxidation states will equal its charge.  If the chemical species is molecular, then the oxidation state is generally assigned according to the Lewis symbol of the active element; the one losing or gaining electrons.  A few nonmetals (e.g. sulfur & phosphorous) and several of the d, p, and f block metals have two or more possible oxidation states.

The Redox Reaction

Reduction is the process of gaining electrons which causes the oxidation state to reduce in value; due to the addition of negative charge.  Oxidation is the loss of electrons which has the effect of an increase in oxidation state value.  Any redox reaction can be separated into a pair of half reactions.  The first half reaction shows a gain of electrons (reduction) and the second half reaction shows a loss of electrons (oxidation).  Each half reaction must show the same number of electrons, so that the electrons will cancel upon adding the two reactions.  Sometimes the number of electrons needs to be modified for one or both half reactions.  The modified half reactions must contain a number of electrons equal to the lowest common multiple of the original numbers of electrons.

Where Do We Find Redox Reactions

Redox reactions are very common and are occurring in such processes as corrosion, electrolysis, electroplating, combustion and life itself.  Yes! - Life is a process!  The overall process of life is a grand combination of complex reaction cycles (many of them redox) working together to keep you alive. One such process is metabolism.  Metabolism is the process of extracting energy from ingested carbohydrates via a "cascading" transfer of electrons culminating in the production of ATP (adenosine triphosphate).  ATP is the "fuel" for other important biochemical processes such as protein production and DNA replication.

That's all for now!  The next few posts will elaborate on some of the concepts introduced in this post.

As always, thank you for reading!

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