Oxidation-reduction reaction

Oxidation Reduction Reaction 2802
Photo by: Giorgio Clementi

The term oxidation-reduction reaction actually refers to two chemical reactions that always occur at the same time: oxidation and reduction. Oxidation-reduction reactions are also referred to more simply as redox reactions. Oxidation, reduction, and redox reactions can all be defined in two ways.

The simpler definitions refer to reactions involving some form of oxygen. As an example, pure iron can be produced from iron oxide in a blast furnace by the following reaction:

3 C + 2 Fe 2 O 3 → 4 Fe + 3 CO 2

In this reaction, iron oxide (Fe 2 O 3 ) gives away its oxygen to carbon (C). In chemical terms, the carbon is said to be oxidized because it has gained oxygen. At the same time, the iron oxide is said to be reduced because it has lost oxygen.

Because of its ability to give away oxygen, iron oxide is called an oxidizing agent. Similarly, because of its ability to take on oxygen, carbon is said to be a reducing agent. Oxidation and reduction always occur together. If one substance gives away oxygen (oxidation), a second substance must be present to take on that oxygen (reduction).

By looking at the above example, you can see that the following statements must always be true:

An oxidizing agent (in this case, iron oxide) is always reduced.

Words to Know

Combustion: An oxidation-reduction reaction that occurs so rapidly that noticeable heat and light are produced.

Corrosion: An oxidation-reduction reaction in which a metal is oxidized and oxygen is reduced, usually in the presence of moisture.

Oxidation: A process in which a chemical substance takes on oxygen or loses electrons.

Oxidizing agent: A chemical substance that gives up oxygen or takes on electrons from another substance.

Reducing agent: A chemical substance that takes on oxygen or gives up electrons to another substance.

Reduction: A process in which a chemical substance gives off oxygen or takes on electrons.

A reducing agent (in this case, carbon) is always oxidized.

Redox and electron exchanges

For many years, chemists thought of oxidation and reduction as involving the element oxygen in some way or another. That's where the name oxidation came from. But they eventually learned that other elements behave chemically in much the same way as oxygen. They decided to revise their definition of oxidation and reduction to make it more general—to apply to elements other than oxygen.

The second definition for oxidation and reduction is not as easy to see. It is based on the fact that when two elements react with each other, they do so by exchanging electrons. In an oxidation-reduction reaction like the one above, the element that is oxidized always loses electrons. The element that is reduced always gains electrons. The more general definition of redox reactions, then, involves the gain and loss of electrons rather than the gain and loss of oxygen.

In the reaction below, for example, sodium metal (Na) reacts with chlorine gas (Cl 2 ) in such a way that sodium atoms lose one electron each to chlorine atoms:

2 Na + Cl 2 → 2 NaCl

Because sodium loses electrons in this reaction, it is said to be oxidized. Because chlorine gains electrons in the reaction, it is said to be reduced.

Types of redox reactions. Redox reactions are among the most common and most important chemical reactions in everyday life. The great majority of those reactions can be classified on the basis of how rapidly they occur. Combustion is an example of a redox reaction that occurs so rapidly that noticeable heat and light are produced. Corrosion, decay, and various biological processes are examples of oxidation that occurs so slowly that noticeable heat and light are not produced.

Combustion. Combustion means burning. Any time a material burns, an oxidation-reduction reaction occurs. The two equations below show what happens when coal (which is nearly pure carbon) and gasoline (C 8 H 18 ) burn. You can see that the fuel is oxidized in each case:

C + O 2 → CO 2

2 C 8 H 18 + 25 O 2 → 16 CO 2 + 18 H 2 O

In reactions such as these, oxidation occurs very rapidly and energy is released. That energy is put to use to heat homes and buildings; to drive automobiles, trucks, ships, airplanes, and trains; to operate industrial processes; and for numerous other purposes.

Rust. Most metals react with oxygen to form compounds known as oxides. Rust is the name given to the oxide of iron and, sometimes, the oxides of other metals. The process by which rusting occurs is also known as corrosion. Corrosion is very much like combustion, except that it occurs much more slowly. The equation below shows perhaps the most common form of corrosion, the rusting of iron.

4 Fe + 3 O 2 → 2 Fe 2 O 3

Decay. The compounds that make up living organisms, such as plants and animals, are very complex. They consist primarily of carbon, oxygen, and hydrogen. A simple way to represent such compounds is to use the letters x, y, and z to show that many atoms of carbon, hydrogen, and oxygen are present in the compounds.

When a plant or animal dies, the organic compounds of which it is composed begin to react with oxygen. The reaction is similar to the combustion of gasoline shown above, but it occurs much more slowly. The process is known as decay, and it is another example of a common oxidation-reduction reaction. The equation below represents the decay (oxidation) of a compound that might be found in a dead plant:

C x H y O z + O 2 → CO 2 + H 2 O

Biological processes. Many of the changes that take place within living organisms are also redox reactions. For example, the digestion of food is an oxidation process. Food molecules react with oxygen in the body to form carbon dioxide and water. Energy is also released in the process. The carbon dioxide and water are eliminated from the body as waste products, but the energy is used to make possible all the chemical reactions that keep an organism alive and help it to grow.

User Contributions:

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Jul 6, 2009 @ 11:11 am
^^ What a great article! It helped me understood the thihng a lot better!!Thanks :3
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Jan 13, 2010 @ 10:22 pm
nice, thanks. Very good information to understand redox reaction in simple manner.
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Jan 31, 2010 @ 3:03 am
can you tell me what are the substances that undergo redox rection?? plzzz.. badly needed
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Feb 3, 2010 @ 6:06 am
hi guys may u pliz help me reduce iron oxide, i believe its also called red oxide from my final product. i operate a small mine where we pick semiprecious stones, the problem we are having is that the ore contains a lot of irons which we dont need. furthermore because we use water in removing surface materials from our stones when it mixes with the irons we get this red oxide that distorts the colour of our stones.
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Feb 4, 2010 @ 6:06 am
hey!!!guys..can u tell me what are substances that undergo redox reaction...its part of our project..please
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May 6, 2010 @ 1:13 pm
it's really nice. it hlped a lot in understanding easily.
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May 28, 2010 @ 11:23 pm
can you please tell what are agents of oxidation and reduction reactions
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Jun 28, 2010 @ 10:22 pm
it is very helpful to the students... specially to us,bio sci majors..
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Aug 11, 2010 @ 6:06 am
should give more simple examples and good examplesthat can be used for the std viii
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Aug 21, 2010 @ 2:02 am
helpful for students like me .. as a pharmacy student
more power
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Aug 31, 2010 @ 6:06 am
Is it correct to define oxidation as an increase in oxidation number as a result of losing electrons?
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Sep 28, 2010 @ 10:10 am
THANKS, can you tell me how to balanced the reduction-oxidation Reaction
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Oct 4, 2010 @ 7:07 am
i like this site, can i get more example of oxidation and reduction example?
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Dec 3, 2010 @ 10:10 am
Ok this site is very well informed, I've come to the conclusion. That it would be very possible to create, a fuel cell. By using the REDOX CH4 in a hybrid hydrogen powered vehicle.
I also think that this type of fuel cell could be the door way to a reinvent of the air powered jet packs of tomorrow. By using this type of cell fuel of CH4 fuel to power the air powered jet pack. Now groups who believe that air propulsion powered vehicles. Could be the next step of things to come by using a methane gas fuel cell.
Maybe will create a fuel cell that the vehicle itself, will make and store its own fuel. Who knows what tomorrow will bring.
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Jan 30, 2011 @ 1:13 pm
Wow this is a very good artical thing, i am doing a assignment on every day reactions this information i will include in it thanks alot for help! I think with this help im gonna do alright ! ;)
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Feb 18, 2011 @ 11:11 am
how can i write a redox reaction from a given chemical equation
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Aug 17, 2011 @ 8:08 am
I think in a blast furnace, carbon monoxide is formed (through a series of reduction-oxidation reactions) from the initial addition of limestone. That carbon monoxide is used in the reaction for molten iron:

Fe2O3 + 3CO -> 2Fe + 3CO2
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Aug 29, 2011 @ 8:20 pm
dat was awesome studies
i think dis article should be recognized and accepted by all
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Nov 6, 2011 @ 2:14 pm
Wow this helped with my paper a ton! It gave me more info then most websites i went to.
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Nov 23, 2011 @ 4:04 am
thanks a lot:)
i found what i really need.it helps me to understand it easily.
freaky nuts
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May 2, 2012 @ 10:10 am
hey guys.i m searching for applications of oxidation reactions in every day life.needed badly
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Jun 4, 2012 @ 10:22 pm
Hi, I am Mohamed and Iam a student. In high school. I proad of to learn chemistry as soon as possible. So how i can learn something like, chemical equestion, chemical formula. And also complete chemistry.
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Jun 5, 2012 @ 2:14 pm
well explained!! Text should be abridged and images, examples should be added.
IN ALL , AVERAGE UNDERSTANDING!! YOU should add animated images!!!
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Feb 5, 2014 @ 9:21 pm
how we can balance the redox teaction of blast furnace
Aprarna C .Therumthanam
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Nov 22, 2014 @ 10:22 pm
please explain redox reaction in biological system

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