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Redox (shorthand for
reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed.
This can be either a simple redox process such as the oxidation of
carbon to yield
carbon dioxide, or the reduction of carbon by
hydrogen to yield methane (CH4), or it can be a complex process such as the oxidation of
sugar in the human body through a series of very complex
electron transfer processes.
The term
redox comes from the two concepts of
reduction and
oxidation. It can be explained in simple terms:
- Oxidation describes the loss of electrons by a molecule, atom or ion
- Reduction describes the gain of electrons by a molecule, atom or ion
However, these descriptions (though sufficient for many purposes) are not truly correct. Oxidation and reduction properly refer to
a change in oxidation number — the actual transfer of electrons may never occur. Thus, oxidation is better defined as an
increase in oxidation number, and reduction as a
decrease in oxidation number. In practice, the transfer of electrons will always cause a change in oxidation number, but there are many reactions which are classed as "redox" even though no electron transfer occurs (such as those involving covalent bonds).
Non-redox reactions, which do not involve changes in
formal charge, are known as Metathesis reaction (chemistry) reactions.
.
Oxidizing and reducing agents
Substances that have the ability to
oxidize other substances are said to be
oxidative and are known as
oxidizing agents,
oxidants or
oxidizers. Put in another way, the oxidant removes electrons from another substance, and is thus reduced itself. And because it "accepts" electrons it is also called an
electron acceptor.
Oxidants are usually chemical substances with elements in high oxidation numbers (e.g.,
hydrogen peroxide,
permanganate, chromium trioxide, Cr2O72−,
Osmium(VIII)_oxide) or highly
electronegativity substances that can gain one or two extra electrons by oxidizing a substance (Oxygen,
Fluorine, Chlorine,
Bromine).
Substances that have the ability to
reduce other substances are said to be
reductive and are known as
reducing agents,
reductants, or
reducers. Put in another way, the reductant transfers electrons to another substance, and is thus oxidized itself. And because it "donates" electrons it is also called an
electron donor. Reductants in chemistry are very diverse.
Metal reduction - electropositive elemental
metals can be used (Li, Na, Mg, Fe, Zn, Al). These metals donate or
give away electrons readily. Other kinds of reductants are
hydride transfer reagents (NaBH4, LiAlH4), these reagents are widely used in
organic chemistry, primarily in the reduction of carbonyl compounds to
alcohols. Another useful method is reductions involving hydrogen gas (H2) with a
palladium,
platinum, or
nickel catalyst. These
catalytic reductions are primarily used in the reduction of carbon-carbon double or triple bonds.
The chemical way to look at redox processes is that
the reductant transfers electrons to the oxidant. Thus, in the reaction, the
reductant or
reducing agent loses electrons and is
oxidized and the
oxidant or
oxidizing agent gains electrons and is
reduced. The pair of an oxidising and reducing agent that are involved in a particular reaction is called a
redox pair.
Oxidation in industry
Oxidation is used in a wide variety of industries such as in the production of cleaning products.
Redox reactions are the foundation of
electrochemical cells.
Examples of redox reactions
A good example is the reaction between
hydrogen and fluorine:
\mathrm{H}_{2} + \mathrm{F}_{2} \longrightarrow 2\mathrm {HF}
We can write this overall reaction as two half-reactions: the oxidation reaction
\mathrm{H}_{2} \longrightarrow 2\mathrm{H}^{+} + 2e^-
and the reduction reaction:
\mathrm{F}_{2} + 2e^- \longrightarrow 2\mathrm{F}^{-}
Analysing each half-reaction in isolation can often make the overall chemical process clearer. Because there is no net change in charge during a redox reaction, the number of electrons in excess in the oxidation reaction must equal the number consumed by the reduction reaction (as shown above).
Elements, even in molecular form, always have an oxidation number of zero. In the first half reaction, hydrogen is oxidized from an oxidation number of zero to an oxidation number of +1. In the second half reaction, fluorine is reduced from an oxidation number of zero to an oxidation number of −1.
When adding the reactions together the electrons cancel:
\frac{\begin{array}{rcl}
\mathrm{H}_{2} & \longrightarrow & 2\mathrm{H}^{+} + 2e^{-}\\\mathrm{F}_{2} + 2e^{-} & \longrightarrow & 2\mathrm{F}^{-}\end{array-->{\begin{array}{rcl}\mathrm{H}_{2} + \mathrm{F}_{2} & \longrightarrow & 2\mathrm{H}^{+} + 2\mathrm{F}^{-}\end{array-->
And the ions combine to form
hydrofluoric acid:
\mathrm{H}_{2} + \mathrm{F}_{2}\, \ \longrightarrow \ 2\mathrm{H}^{+} + 2\mathrm{F}^{-}\ \longrightarrow \ 2\mathrm{HF}
Other examples
- iron(II) oxidizes to iron(III):
Fe2+ → Fe3+ + e−
H2O2 + 2 e− → 2 OH−
overall equation for the above:
2Fe2+ + H2O2 + 2H+ → 2Fe3+ + 2H2O
2NO3− + 10e− + 12 H+ → N2 + 6H2O
- iron oxidizes to iron(III) oxide and oxygen is reduced forming iron(III) oxide (commonly known as rusting, which is similar to tarnishing):
4Fe + 3O2 → 2 Fe2O3
- Combustion of hydrocarbons, e.g. in an internal combustion engine, produces water, carbon dioxide, some partially oxidized forms such as carbon monoxide and heat energy. Complete oxidation of materials containing carbon produces carbon dioxide.
- In organic chemistry, stepwise oxidation of a hydrocarbon produces water and, successively, an alcohol, an aldehyde or a ketone, carboxylic acid, and then a peroxide.
- In biology many important processes involve redox reactions. Cell respiration, for instance, is the oxidation of glucose (C6H12O6) to carbon dioxide and the reduction of oxygen to water. The summary equation for cell respiration is:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
The process of cell respiration also depends heavily on the reduction of NAD+ to NADH and the reverse reaction (the oxidation of NADH to NAD+).
Photosynthesis is essentially the reverse of the redox reaction in cell respiration:
6 CO2 + 6 H2O +
photon → C6H12O6 + 6 O2
Redox reactions in biology
{|border="0" width=150px border="0" cellpadding="2" cellspacing="0" style="font-size: 85%; border: 1px solid #CCCCCC; margin: 0.3em;"||}{|border="0" width=150px border="0" cellpadding="2" cellspacing="0" style="font-size: 85%; border: 1px solid #CCCCCC; margin: 0.3em;"||}Top: ascorbic acid (reducing agent of Vitamin C)
Bottom: dehydroascorbic acid (oxidizing agent of
Vitamin C)Much
biology energy is stored and released by means of redox reactions. Photosynthesis involves the reduction of
carbon dioxide into
sugars and the oxidation of
water (molecule) into molecular
oxygen. The reverse reaction, Cellular respiration, oxidizes sugars to produce carbon dioxide and water. As intermediate steps, the reduced carbon compounds are used to reduce
nicotinamide adenine dinucleotide (NAD+), which then contributes to the creation of a
proton gradient, which drives the synthesis of
adenosine triphosphate (ATP) and is maintained by the reduction of oxygen.In animal cells,
mitochondria perform similar functions. See
Membrane potential article.
The term
redox state is often used to describe the balance of Nicotinamide adenine dinucleotide and Nicotinamide adenine dinucleotide phosphate in a biological system such as a cell or organ. The redox state is reflected in the balance of several sets of metabolites (e.g.,
lactate and
pyruvate,
beta-hydroxybutyrate and acetoacetate) whose interconversion is dependent on these ratios. An abnormal redox state can develop in a variety of deleterious situations, such as Hypoxia (medical), Shock (medical), and sepsis.
Redox signaling involves the control of cellular processes by redox processes.
Redox cycling
A wide variety of aromaticity are enzyme reduced to form Radical (chemistry) that contain one more electron than their parent compounds. In general, the electron donor is any of a wide variety of
flavoenzymes and their coenzymes. Once formed, these anion free radicals reduce molecular oxygen to
superoxide and regenerate the unchanged parent compound. The net reaction is the oxidation of the flavoenzyme's coenzymes and the reduction of molecular oxygen to form superoxide. This catalytic behavior has been described as futile cycle or redox cycling.
Examples of redox cycling-inducing molecules are the
herbicide paraquat and other viologens and
quinones such as
menadione.
References
See also
External links
- Redox reactions calculator
- Redox reactions at Chemguide
- Online redox reaction equation balancer, balances equations of any half-cell and full reactions
Redox (shorthand for
reduction/oxidation reaction) describes all
chemical reactions in which atoms have their oxidation number (
oxidation state) changed.
This can be either a simple redox process such as the oxidation of
carbon to yield carbon dioxide, or the reduction of carbon by hydrogen to yield
methane (CH4), or it can be a complex process such as the oxidation of sugar in the human body through a series of very complex
electron transfer processes.
The term
redox comes from the two concepts of
reduction and
oxidation. It can be explained in simple terms:
- Oxidation describes the loss of electrons by a molecule, atom or ion
- Reduction describes the gain of electrons by a molecule, atom or ion
However, these descriptions (though sufficient for many purposes) are not truly correct. Oxidation and reduction properly refer to
a change in oxidation number — the actual transfer of electrons may never occur. Thus, oxidation is better defined as an
increase in oxidation number, and reduction as a
decrease in oxidation number. In practice, the transfer of electrons will always cause a change in oxidation number, but there are many reactions which are classed as "redox" even though no electron transfer occurs (such as those involving covalent bonds).
Non-redox reactions, which do not involve changes in
formal charge, are known as
Metathesis reaction (chemistry) reactions.
.
Oxidizing and reducing agents
Substances that have the ability to
oxidize other substances are said to be
oxidative and are known as
oxidizing agents,
oxidants or
oxidizers. Put in another way, the oxidant removes electrons from another substance, and is thus reduced itself. And because it "accepts" electrons it is also called an
electron acceptor.
Oxidants are usually chemical substances with elements in high oxidation numbers (e.g.,
hydrogen peroxide,
permanganate,
chromium trioxide, Cr2O72−, Osmium(VIII)_oxide) or highly electronegativity substances that can gain one or two extra electrons by oxidizing a substance (Oxygen, Fluorine, Chlorine,
Bromine).
Substances that have the ability to
reduce other substances are said to be
reductive and are known as
reducing agents,
reductants, or
reducers. Put in another way, the reductant transfers electrons to another substance, and is thus oxidized itself. And because it "donates" electrons it is also called an
electron donor. Reductants in chemistry are very diverse.
Metal reduction - electropositive elemental
metals can be used (Li, Na, Mg, Fe, Zn, Al). These metals donate or
give away electrons readily. Other kinds of reductants are
hydride transfer reagents (NaBH4, LiAlH4), these reagents are widely used in
organic chemistry, primarily in the reduction of
carbonyl compounds to alcohols. Another useful method is reductions involving hydrogen gas (H2) with a palladium, platinum, or
nickel catalyst. These
catalytic reductions are primarily used in the reduction of carbon-carbon double or triple bonds.
The chemical way to look at redox processes is that
the reductant transfers electrons to the oxidant. Thus, in the reaction, the
reductant or
reducing agent loses electrons and is
oxidized and the
oxidant or
oxidizing agent gains electrons and is
reduced. The pair of an oxidising and reducing agent that are involved in a particular reaction is called a
redox pair.
Oxidation in industry
Oxidation is used in a wide variety of industries such as in the production of cleaning products.
Redox reactions are the foundation of
electrochemical cells.
Examples of redox reactions
A good example is the reaction between hydrogen and
fluorine:
\mathrm{H}_{2} + \mathrm{F}_{2} \longrightarrow 2\mathrm {HF}
We can write this overall reaction as two half-reactions: the oxidation reaction
\mathrm{H}_{2} \longrightarrow 2\mathrm{H}^{+} + 2e^-
and the reduction reaction:
\mathrm{F}_{2} + 2e^- \longrightarrow 2\mathrm{F}^{-}
Analysing each half-reaction in isolation can often make the overall chemical process clearer. Because there is no net change in charge during a redox reaction, the number of electrons in excess in the oxidation reaction must equal the number consumed by the reduction reaction (as shown above).
Elements, even in molecular form, always have an oxidation number of zero. In the first half reaction, hydrogen is oxidized from an oxidation number of zero to an oxidation number of +1. In the second half reaction, fluorine is reduced from an oxidation number of zero to an oxidation number of −1.
When adding the reactions together the electrons cancel:
\frac{\begin{array}{rcl}
\mathrm{H}_{2} & \longrightarrow & 2\mathrm{H}^{+} + 2e^{-}\\\mathrm{F}_{2} + 2e^{-} & \longrightarrow & 2\mathrm{F}^{-}\end{array-->{\begin{array}{rcl}\mathrm{H}_{2} + \mathrm{F}_{2} & \longrightarrow & 2\mathrm{H}^{+} + 2\mathrm{F}^{-}\end{array-->
And the ions combine to form hydrofluoric acid:
\mathrm{H}_{2} + \mathrm{F}_{2}\, \ \longrightarrow \ 2\mathrm{H}^{+} + 2\mathrm{F}^{-}\ \longrightarrow \ 2\mathrm{HF}
Other examples
- iron(II) oxidizes to iron(III):
Fe2+ → Fe3+ + e−
H2O2 + 2 e− → 2 OH−
overall equation for the above:
2Fe2+ + H2O2 + 2H+ → 2Fe3+ + 2H2O
2NO3− + 10e− + 12 H+ → N2 + 6H2O
- iron oxidizes to iron(III) oxide and oxygen is reduced forming iron(III) oxide (commonly known as rusting, which is similar to tarnishing):
4Fe + 3O2 → 2 Fe2O3
- Combustion of hydrocarbons, e.g. in an internal combustion engine, produces water, carbon dioxide, some partially oxidized forms such as carbon monoxide and heat energy. Complete oxidation of materials containing carbon produces carbon dioxide.
- In organic chemistry, stepwise oxidation of a hydrocarbon produces water and, successively, an alcohol, an aldehyde or a ketone, carboxylic acid, and then a peroxide.
- In biology many important processes involve redox reactions. Cell respiration, for instance, is the oxidation of glucose (C6H12O6) to carbon dioxide and the reduction of oxygen to water. The summary equation for cell respiration is:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
The process of cell respiration also depends heavily on the reduction of NAD+ to NADH and the reverse reaction (the oxidation of NADH to NAD+).
Photosynthesis is essentially the reverse of the redox reaction in cell respiration:
6 CO2 + 6 H2O +
photon → C6H12O6 + 6 O2
Redox reactions in biology
{|border="0" width=150px border="0" cellpadding="2" cellspacing="0" style="font-size: 85%; border: 1px solid #CCCCCC; margin: 0.3em;"||}{|border="0" width=150px border="0" cellpadding="2" cellspacing="0" style="font-size: 85%; border: 1px solid #CCCCCC; margin: 0.3em;"||}Top:
ascorbic acid (
reducing agent of
Vitamin C)
Bottom: dehydroascorbic acid (oxidizing agent of Vitamin C)Much
biology energy is stored and released by means of redox reactions.
Photosynthesis involves the reduction of carbon dioxide into
sugars and the oxidation of
water (molecule) into molecular oxygen. The reverse reaction, Cellular respiration, oxidizes sugars to produce carbon dioxide and water. As intermediate steps, the reduced carbon compounds are used to reduce nicotinamide adenine dinucleotide (NAD+), which then contributes to the creation of a
proton gradient, which drives the synthesis of
adenosine triphosphate (ATP) and is maintained by the reduction of oxygen.In animal cells,
mitochondria perform similar functions. See
Membrane potential article.
The term
redox state is often used to describe the balance of Nicotinamide adenine dinucleotide and Nicotinamide adenine dinucleotide phosphate in a biological system such as a cell or organ. The redox state is reflected in the balance of several sets of metabolites (e.g., lactate and pyruvate,
beta-hydroxybutyrate and acetoacetate) whose interconversion is dependent on these ratios. An abnormal redox state can develop in a variety of deleterious situations, such as
Hypoxia (medical), Shock (medical), and sepsis. Redox signaling involves the control of cellular processes by redox processes.
Redox cycling
A wide variety of
aromaticity are enzyme reduced to form
Radical (chemistry) that contain one more electron than their parent compounds. In general, the electron donor is any of a wide variety of
flavoenzymes and their coenzymes. Once formed, these anion free radicals reduce molecular oxygen to
superoxide and regenerate the unchanged parent compound. The net reaction is the oxidation of the flavoenzyme's coenzymes and the reduction of molecular oxygen to form superoxide. This catalytic behavior has been described as futile cycle or redox cycling.
Examples of redox cycling-inducing molecules are the
herbicide paraquat and other viologens and
quinones such as menadione.
References
See also
External links
- Redox reactions calculator
- Redox reactions at Chemguide
- Online redox reaction equation balancer, balances equations of any half-cell and full reactions
High Temperature Oxidation Group
Welcome to the High Temperature Oxidation and Coatings group at the University of Birmingham. These pages are designed to let you know about the group in terms of the people ...
Redox - Wikipedia, the free encyclopedia
Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed.
Definition: oxidation from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.
Definition: oxidation pond from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.
Oxidation Chemistry
This template was created by Magnus W. Walter and last updated on 24 September 2006. ... Oxidation Chemistry Reading and Literature References. Oxford Chemistry Primer: T.
Sheffield ChemPuter
Chemputer calculates such as isotope patterns, element percentages, molecular shape, oxidation state, etc. Chemputer calculates such as isotope patterns, element percentages ...
oxidation of alcohols
Oxidation of alcohols using acidified sodium or potassium dichromate(VI) solution. ... This page looks at the oxidation of alcohols using acidified sodium or potassium dichromate ...
oxidation of aldehydes and ketones
The use of oxidation reactions to distinguish between aldehydes and ketones ... This page looks at ways of distinguishing between aldehydes and ketones using oxidising agents such ...
oxidation (chemistry) - Hutchinson encyclopedia article about ...
Hutchinson encyclopedia article about oxidation (chemistry). oxidation (chemistry). Information about oxidation (chemistry) in the Hutchinson encyclopedia.
Oxidation Therapy
Healing and prevention, incorporating eastern and western philosophies, using medical grade ozone. About, treatments and contact.
