Keerpunt Terug Naar de Winnende Formule Voor de Definitie Van de Term Chemische Reiniging Tips...

8/14/2019 Keerpunt Terug Naar de Winnende Formule Voor de Definitie Van de Term Chemische Reiniging Tips Chemische Reiniging Stellingen Namen Winnaar Van N

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oxidation and reduction, complementary chemical reactions characterized by the loss or gain,

respectively, of one or more electrons by an atom or molecule. Originally the term oxidation was

used to refer to a reaction in which oxygen combined with an element or compound, e.g., thereaction of magnesium with oxygen to form magnesium oxide or the combination of carbon

monoxide with oxygen to form carbon dioxide. Similarly, reduction referred to a decrease in the

amount of oxygen in a substance or its complete removal, e.g., the reaction of cupric oxide andhydrogen to form copper and water.

When an atom or molecule combines with oxygen, it tends to give up electrons to the oxygen in

forming a chemical bond. Similarly, when it loses oxygen, it tends to gain electrons. Such

changes are now described in terms of changes in the oxidation number, or oxidation state, of theatom or molecule (see valence). Thus oxidation has come to be defined as a loss of electrons or

an increase in oxidation number, while reduction is defined as a gain of electrons or a decrease in

oxidation number, whether or not oxygen itself is actually involved in the reaction.

In the formation of magnesium oxide from magnesium and oxygen, the magnesium atoms havelost two electrons, or the oxidation number has increased from zero to +2. This is also true when

magnesium reacts with chlorine to form magnesium chloride. In solution, ferrous iron (oxidation

number +2) may be oxidized to ferric iron (oxidation number +3) by the loss of an electron. Inthe reduction of cupric oxide the oxidation number of copper has changed from +2 to zero by the

gain of two electrons. The two processes, oxidation and reduction, occur simultaneously and in

chemically equivalent quantities. In the formation of magnesium chloride, for every magnesium

atom oxidized by a loss of two electrons, two chlorine atoms are reduced by a gain of oneelectron each.

Oxidation-reduction reactions, called also redox reactions, are most simply balanced in the form

of chemical equations by arranging the quantities of the substances involved so that the numberof electrons lost by one substance is equaled by the number gained by another substance. In such

reactions, the substance losing electrons (undergoing oxidation) is said to be an electron donor,

or reductant, since its lost electrons are given to and reduce the other substance. Conversely, the

substance that is gaining electrons (undergoing reduction) is said to be an electron acceptor, oroxidant.

Common reductants (substances readily oxidized) are the active metals, hydrogen, hydrogen

sulfide, carbon, carbon monoxide, and sulfurous acid. Common oxidants (substances readily

reduced) include the halogens (especially fluorine and chlorine), oxygen, ozone, potassiumpermanganate, potassium dichromate, nitric acid, and concentrated sulfuric acid. Some

substances are capable of acting either as reductants or as oxidants, e.g., hydrogen peroxide andnitrous acid.

The corrosion of metals is a naturally occurring redox reaction. Industrially, many redox

reactions are of great importance: combustionof fuels; electrolysis (oxidation occurs at the

anode and reduction at the cathode); and metallurgical processes in which free metals are

obtained from their ores.
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WordNet: redox

Top

Home > Library > Literature & Language >WordNetNote: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: a reversible chemical reaction in which one reaction is an oxidation and the reverseis a reduction

Synonyms: oxidation-reduction, oxidoreduction

Wikipedia: Redox

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Home > Library > Miscellaneous> Wikipedia

Illustration of a redox reaction

Redox (shorthand forreduction-oxidation reaction) describes all chemical reactionsin which

atoms have theiroxidation number(oxidation state) changed. This can be either a simple redox

process such as the oxidation ofcarbon to yield carbon dioxide or the reduction of carbon byhydrogen to yield methane (CH4), or it can be a complex process such as the oxidation ofsugar

in the human body through a series of very complex electron transferprocesses.

The term redox comes from the two concepts ofreduction and oxidation. It can be explained in

simple terms:

Oxidation describes the loss ofelectrons or an increase in oxidation state by amolecule,

atom orion.

Reduction describes thegain of electrons or a decrease in oxidation state by a molecule,atom or ion.

Though sufficient for many purposes, these descriptions are not precisely 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 reductionas a decrease in oxidation number. In practice, the transfer of electrons will always cause a

change in oxidation number, but there are many reactions that are classed as "redox" even though

no electron transfer occurs (such as those involving covalent bonds).
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Non-redox reactions, which do not involve changes in formal charge, are known as metathesis

reactions.

The two parts of a redox reaction

Rusting iron

Abonfire.Combustion consists of redox reactions involvingfree radicals.

Contents

[hide]

1 Oxidizing and reducing agents

o 1.1 Oxidizerso 1.2 Reducers

2 Examples of redox reactionso 2.1 Displacement reactions

o 2.2 Other examples

3 Redox reactions in industry 4 Redox reactions in biology

o 4.1 Redox cycling
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5 Balancing redox reactions

o 5.1 Acidic media

o 5.2 Basic media

6 See also

7 References

8 External links

Oxidizing and reducing agents

The chemical way to look at redox processes is that the reductant transfers electrons to the

oxidant. Thus, in the reaction, the reductant orreducing agentloses electrons and is oxidized,

and the oxidant oroxidizing agentgains electrons and is reduced. The pair of an oxidizing andreducing agent that are involved in a particular reaction is called a redox pair.

Oxidizers

Substances that have the ability to oxidize other substances are said to be oxidative and are

known as oxidizing agents, oxidants, oroxidizers. Put another way, the oxidant removes

electrons from another substance, and is thus itself reduced. 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., H2O2,

MnO4, CrO3, Cr2O7

2, OsO4) or highly electronegative substances that can gain one or two extra

electrons by oxidizing a substance (O,F, Cl,Br).

Reducers

Substances that have the ability to reduce other substances are said to be reductive and are

known as reducing agents,reductants, orreducers. Put in another way, the reductant transferselectrons 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 orgive away electrons readily. Reactions-Reducing AgentsOther kinds of reductants are hydride

transfer reagents (NaBH4, LiAlH4), these reagents are widely used inorganic chemistry[1] [2] ,

primarily in the reduction ofcarbonyl compounds toalcohols. Another useful method is

reductions involving hydrogen gas (H2) with apalladium,platinum, ornickelcatalyst. Thesecatalytic reductions are primarily used in the reduction of carbon-carbon double or triple bonds.

Examples of redox reactions

A good example is the reaction betweenhydrogen and fluorine:

H2 + F2 2 HF
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We can write this overall reaction as two half-reactions: the oxidation reaction:

H2 2 H+ + 2 e

and the reduction reaction:

F2 + 2 e 2 F

Analyzing 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:

H2 2 H+ + 2 e

F2 + 2 e 2 F

H2 + F2 2 H+ + 2 F

And the ions combine to form hydrogen fluoride:

H2 + F2 2 H+ + 2 F 2 HF

Displacement reactions

Redox occurs in single displacement reactionsorsubstitution reactions. The redox component of

these types of reactions is the change of oxidation state (charge) on certain atoms, not the actualexchange of atoms in the compounds.

For example, in the reaction between ironand copper(II) sulfatesolution:

Fe + CuSO4 FeSO4 + Cu

The ionic equation for this reaction is:

Fe + Cu2+ Fe2+ + Cu

As two half-equations, it is seen that the iron is oxidized:

Fe Fe2+ + 2 e
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And the copper is reduced:

Cu2+ + 2 e Cu

Other examples

The oxidation of iron(II) to iron(III) by hydrogen peroxidein the presence of an acid:

Fe2+ Fe3+ + e

H2O2 + 2 e 2 OH

Overall equation:

2 Fe2+ + H2O2 + 2 H+ 2 Fe3+ + 2 H2O

The reduction ofnitrate to nitrogen in the presence of an acid (denitrification):

2 NO3 + 10 e + 12 H+ N2 + 6 H2O

Oxidation of elemental iron to iron(III) oxide by oxygen (commonly known asrusting,which is similar to tarnishing):

4 Fe + 3 O2 2 Fe2O3

The combustion ofhydrocarbons, such as in aninternal combustion engine, which

produces water, carbon dioxide, some partially oxidized forms such as carbon monoxideand heat energy. Complete oxidation of materials containingcarbonproduces carbon

dioxide.

In organic chemistry, the stepwise oxidation of a hydrocarbon by oxygen produces waterand, successively, analcohol, an aldehyde or a ketone, a carboxylic acid, and then aperoxide.

Redox reactions in industry

The primary process of reducing ore to produce metals is discussed in the article on Smelting.

Oxidation is used in a wide variety of industries such as in the production of cleaning products

and oxidising ammonia to produce nitric acid, which is used in most fertilizers.

Redox reactions are the foundation ofelectrochemical cells.

The production of compact discs depends on a redox reaction, which coats the disc with a thin

layer of metal film.

Redox reactions in biology
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Top:ascorbic acid (reduced formofVitamin C)

Bottom:dehydroascorbic acid(oxidized form ofVitamin C)

Many importantbiological processes involve redox reactions.

Cellular respiration, for instance, is the oxidation ofglucose (C6H12O6) toCO2 and the reduction

ofoxygen 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 ofNAD

+

to NADH and thereverse reaction (the oxidation of NADH to NAD+). Photosynthesisis essentially the reverse ofthe redox reaction in cell respiration:

6 CO2 + 6 H2O +light energy C6H12O6 + 6 O2

Biological energy is frequently stored and released by means of redox reactions. Photosynthesis

involves the reduction ofcarbon dioxideinto sugars and the oxidation ofwaterinto molecularoxygen. The reverse reaction, 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 aproton gradient, which drives

the synthesis ofadenosine triphosphate (ATP) and is maintained by the reduction of oxygen. Inanimal cells, mitochondria perform similar functions. SeeMembrane potentialarticle.

The term redox state is often used to describe the balance ofNAD+/NADH andNADP+/NADPH

in a biological system such as a cell or organ. The redox state is reflected in the balance ofseveral sets of metabolites (e.g.,lactate andpyruvate,beta-hydroxybutyrate and acetoacetate),

whose interconversion is dependent on these ratios. An abnormal redox state can develop in a
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variety of deleterious situations, such as hypoxia,shock, and sepsis.Redox signaling involves

the control of cellular processes by redox processes.

Redox proteins and their genes must be Co-located forRedox Regulation according to the CoRRHypothesis for the function of DNA in mitochondria and chloroplasts.

Redox cycling

A wide variety ofaromatic compounds are enzymatically reduced to form free radicals that

contain one more electron than their parent compounds. In general, the electron donor is any of a

wide variety of flavoenzymes and theircoenzymes. Once formed, these anion free radicals

reduce molecular oxygen tosuperoxide, and regenerate the unchanged parent compound. The netreaction 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 herbicideparaquat and otherviologens

andquinones such as menadione.[3]

Balancing redox reactions

Describing the overall electrochemical reaction for a redox process requires a balancingof the

component half-reactionsfor oxidation and reduction. For reactions in aqueous solution, thisgenerally involves adding H+ ,OH , H2O, and electrons to compensate for the oxidation changes.

Acidic media

In acidic media, H+ ions and water are added to half reactions to balance the overall reaction.

For example, when manganese(II) reacts with sodium bismuthate:

Unbalanced reaction: Mn2+ (aq) + NaBiO3 (s) Bi3+ (aq) + MnO4

(aq)

Oxidation: 4 H2O (l) + Mn2+ (aq) MnO4

(aq) + 8 H+ (aq) + 5 e

Reduction: 2 e + 6 H+ + BiO3 (s) Bi3+ (aq) + 3 H2O (l)

The reaction is balanced by scaling the two half-cell reactions to involve the same number of

electrons (multiplying the oxidation reaction by the number of electrons in the reduction step andvice versa):

8 H2O (l) + 2 Mn2+ (aq) 2 MnO4

(aq) + 16 H+ (aq) + 10 e

10 e + 30 H+ + 5 BiO3 (s) 5 Bi3+ (aq) + 15 H2O (l)

Adding these two reactions eliminates the electrons terms and yields the balanced reaction:

14 H+ (aq) + 2 Mn2+ (aq) + 5 NaBiO3 (s) 7 H2O (l) + 2 MnO4 (aq) + 5 Bi3+ (aq) + 5

Na+ (aq)
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Basic media

In basic media, OH ions and water are added to half reactions to balance the overall reaction.

For example, in the reaction betweenpotassium permanganate and sodium sulfite:

Unbalanced reaction: KMnO4 + Na2SO3 + H2O MnO2 + Na2SO4 + KOH

Reduction: 3 e + 2 H2O + MnO4 MnO2 + 4 OH

Oxidation: 2 OH + SO32 SO4

2 + H2O + 2 e

Balancing the number of electrons in the two half-cell reactions gives:

6 e + 4 H2O + 2 MnO4 2 MnO2 + 8 OH

6 OH + 3 SO32 3 SO4

2 + 3 H2O + 6 e

Adding these two half-cell reactions together gives the balanced equation:

2 KMnO4 + 3 Na2SO3 + H2O 2 MnO2 + 3 Na2SO4 + 2 KOH

See also

Organic redox reaction

Hydrogenation

Bessemer process

Bioremediation

Calvin cycle

Citric acid cycle Electrochemical cell Electrochemistry

Chemical looping combustion

Electrochemical series

Galvanic cell

Membrane potential

Oxidative addition and reductive elimination

Reducing agent

Thermic reaction Partial oxidation Reduction potential

Chemical equation

Reduced gas

References

1. ^ Hudlick, Milo (1996).Reductions in Organic Chemistry. Washington, D.C.:

American Chemical Society. pp. 429. ISBN 0-8412-3344-6.

2. ^ Hudlick, Milo (1990). Oxidations in Organic Chemistry. Washington, D.C.:American Chemical Society. pp. 456. ISBN 0-8412-1780-7.

3. ^ "gutier.doc". http://www.bioscience.org/2000/v5/d/gutier/gutier.pdf. Retrieved 2008-

06-30.PDF (2.76MiB)

Schring, J., Schulz, H. D., Fischer, W. R., Bttcher, J., Duijnisveld, W. H. (editors)(1999). Redox: Fundamentals, Processes and Applications, Springer-Verlag, Heidelberg,

246 pp. ISBN 978-3540665281(pdf 3,6 MB)
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UC Berkeley video lecture on redox reactions Redox reactions calculator

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reactions

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The noun has one meaning:

Meaning #1: the conversion of a compound into an isomer of itself

Synonym: isomerization

English

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5min Related Video: Isomerisation

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Wikipedia: Isomerisation


In chemistryisomerisation is the process by which one moleculeis transformed into another

molecule which has exactly the same atoms, but the atoms are rearranged e.g. A-B-C B-A-C

(these related molecules are known as isomers[1]). In some molecules and under some

conditions, isomerisation occurs spontaneously. Many isomers are equal or roughly equal inbond energy, and so exist in roughly equal amounts, provided that they can interconvert
http://www.answers.com/topic/isomerization-isomerisationhttp://www.answers.com/topic/isomerization-wordnethttp://dropdown%28%27langslist%27%29/http://wiki.answers.com/Q/NEWQhttp://wiki.answers.com/Q/NEWQhttp://wiki.answers.com/Q/Special:RecentQhttp://www.answers.com/main/what_content.jsphttp://www.answers.com/main/what_content.jsphttp://wiki.answers.com/Q/NEWQhttp://wiki.answers.com/Q/NEWQhttp://wiki.answers.com/Q/Special:RecentQhttp://wiki.answers.com/Q/Special:RecentAhttp://www.answers.com/main/what_content.jsphttp://www.answers.com/library/Wikipedia-cid-2460443http://www.answers.com/http://www.answers.com/main/what_content.jsphttp://www.answers.com/main/reference.jsphttp://www.answers.com/main/reference.jsphttp://www.answers.com/library/Wikipedia-cid-2460443http://www.answers.com/topic/analytical-chemistryhttp://www.answers.com/topic/analytical-chemistryhttp://www.answers.com/topic/moleculehttp://www.answers.com/topic/moleculehttp://www.answers.com/topic/isomerhttp://www.answers.com/topic/isomerisation#cite_note-0http://www.answers.com/topic/isomerisation#cite_note-0http://www.answers.com/topic/bond-energyhttp://reference.answers.com/http://www.answers.com/http://www.answers.com/topic/isomerization-isomerisationhttp://www.answers.com/topic/isomerization-wordnethttp://dropdown%28%27langslist%27%29/http://wiki.answers.com/Q/NEWQhttp://wiki.answers.com/Q/Special:RecentQhttp://www.answers.com/main/what_content.jsphttp://wiki.answers.com/Q/NEWQhttp://wiki.answers.com/Q/Special:RecentQhttp://wiki.answers.com/Q/Special:RecentAhttp://www.answers.com/main/what_content.jsphttp://www.answers.com/library/Wikipedia-cid-2460443http://www.answers.com/http://www.answers.com/main/what_content.jsphttp://www.answers.com/main/reference.jsphttp://www.answers.com/library/Wikipedia-cid-2460443http://www.answers.com/topic/analytical-chemistryhttp://www.answers.com/topic/moleculehttp://www.answers.com/topic/isomerhttp://www.answers.com/topic/isomerisation#cite_note-0http://www.answers.com/topic/bond-energy


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relatively freely, that is the energy barrier between the two isomers is not too high. When the

isomerisation occurs intramolecularlyit is considered a rearrangement reaction.

Instances of Isomerization

Isomerisations in hydrocarbon cracking. This is usually employed in organic chemistry,where fuels, such aspentane, a straight-chain isomer, are heated in the presence of a

platinum catalyst. The resulting mixture of straight- and branched-chain isomers then

have to be separated. An industrial process is also the isomerisation ofn-butaneintoisobutane.

Trans-cis isomerism. In certain compounds an interconversion ofcis and trans isomerscan be observed, for instance, with maleic acid and withazobenzene often by

photoisomerization. An example is the photochemical conversion of the trans isomer to

the cis isomer ofresveratrol[2]:

Aldose-ketose isomerism in biochemistry.

Isomerisations between conformational isomers. These take place without an actual

rearrangement for instance inconversion of twocyclohexane conformations

Fluxional molecules display rapid interconversion of isomers e.g. Bullvalene.

The energy difference between two isomers is called isomerisation energy. Isomerisations with

low energy difference both experimental and computational (in parentheses) are endothermictrans-cis isomerisation of2-butenewith 2.6 (1.2) kcal/mol, cracking ofisopentaneton-pentanewith 3.6 (4.0) kcal/mol or conversion oftrans-2-buteneto1-butene with 2.6 (2.4) kcal/mol.[3]

References

1. ^ Gold Bookdefinition: Link
http://www.answers.com/topic/intramolecularhttp://www.answers.com/topic/intramolecularhttp://www.answers.com/topic/rearrangement-reactionhttp://www.answers.com/topic/crackinghttp://www.answers.com/topic/crackinghttp://www.answers.com/topic/organic-chemistryhttp://www.answers.com/topic/organic-chemistryhttp://www.answers.com/topic/pentanehttp://www.answers.com/topic/butanehttp://www.answers.com/topic/butanehttp://www.answers.com/topic/isobutanehttp://www.answers.com/topic/cis-trans-isomerism-1http://www.answers.com/topic/cis-trans-isomerism-1http://www.answers.com/topic/maleic-acidhttp://www.answers.com/topic/azobenzenehttp://www.answers.com/topic/azobenzenehttp://www.answers.com/topic/photoisomerizationhttp://www.answers.com/topic/resveratrolhttp://www.answers.com/topic/isomerisation#cite_note-1http://www.answers.com/topic/lobry-de-bruyn-van-ekenstein-transformationhttp://www.answers.com/topic/conformational-isomerhttp://www.answers.com/topic/cyclohexane-conformationhttp://www.answers.com/topic/cyclohexane-conformationhttp://www.answers.com/topic/fluxional-moleculehttp://www.answers.com/topic/bullvalenehttp://www.answers.com/topic/bullvalenehttp://www.answers.com/topic/endothermichttp://www.answers.com/topic/2-butenehttp://www.answers.com/topic/2-butenehttp://www.answers.com/topic/caloriehttp://www.answers.com/topic/molehttp://www.answers.com/topic/isopentanehttp://www.answers.com/topic/isopentanehttp://www.answers.com/topic/pentanehttp://www.answers.com/topic/pentanehttp://www.answers.com/topic/2-butenehttp://www.answers.com/topic/2-butenehttp://www.answers.com/topic/1-butenehttp://www.answers.com/topic/1-butenehttp://www.answers.com/topic/isomerisation#cite_note-2http://www.answers.com/topic/isomerisation#cite_ref-0http://www.answers.com/topic/compendium-of-chemical-terminologyhttp://www.iupac.org/goldbook/I03295.pdfhttp://en.wikipedia.org/wiki/File:Rasveratrol_isomerization.pnghttp://en.wikipedia.org/wiki/File:N-pentane_isomerization.svghttp://www.answers.com/topic/intramolecularhttp://www.answers.com/topic/rearrangement-reactionhttp://www.answers.com/topic/crackinghttp://www.answers.com/topic/organic-chemistryhttp://www.answers.com/topic/pentanehttp://www.answers.com/topic/butanehttp://www.answers.com/topic/isobutanehttp://www.answers.com/topic/cis-trans-isomerism-1http://www.answers.com/topic/maleic-acidhttp://www.answers.com/topic/azobenzenehttp://www.answers.com/topic/photoisomerizationhttp://www.answers.com/topic/resveratrolhttp://www.answers.com/topic/isomerisation#cite_note-1http://www.answers.com/topic/lobry-de-bruyn-van-ekenstein-transformationhttp://www.answers.com/topic/conformational-isomerhttp://www.answers.com/topic/cyclohexane-conformationhttp://www.answers.com/topic/fluxional-moleculehttp://www.answers.com/topic/bullvalenehttp://www.answers.com/topic/endothermichttp://www.answers.com/topic/2-butenehttp://www.answers.com/topic/caloriehttp://www.answers.com/topic/molehttp://www.answers.com/topic/isopentanehttp://www.answers.com/topic/pentanehttp://www.answers.com/topic/2-butenehttp://www.answers.com/topic/1-butenehttp://www.answers.com/topic/isomerisation#cite_note-2http://www.answers.com/topic/isomerisation#cite_ref-0http://www.answers.com/topic/compendium-of-chemical-terminologyhttp://www.iupac.org/goldbook/I03295.pdf


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2. ^Resveratrol Photoisomerization: An Integrative Guided-Inquiry ExperimentElyse

Bernard, Philip Britz-McKibbin, Nicholas Gernigon Vol. 84 No. 7 July 2007Journal of

Chemical Education 11593. ^How to Compute Isomerization Energies of Organic Molecules with Quantum

Chemical Methods Stefan Grimme, Marc Steinmetz, and Martin Korth J. Org. Chem.;

2007; 72(6) pp 2118 - 2126; (Article) doi:10.1021/jo062446p

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been

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Carbon dioxide

Home > Library > Science> Sci-Tech Encyclopedia

A colorless, odorless, tastelessgas, formula CO2, about 1.5 times as heavy as air. Under normal

conditions, it is stable, inert, and nontoxic. The decay (slow oxidation) of all organic materialsproduces CO2. Fresh air contains approximately 0.033% CO2 by volume. In the respiratory

action (breathing) of all animals and humans, CO2 is exhaled.

Carbon dioxide gas may be liquefied or solidified. Solid CO2 is known as dry ice. Carbon

dioxide is obtained commercially from four sources: gas wells, fermentation, combustion ofcarbonaceousfuels, and as a by-product of chemical processing. Applications include use as a
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refrigerant, in either solid or liquid form, inerting medium, chemical reactant, neutralizing agent

for alkalies, and pressurizing agent.

Most CO2 is obtained as a by-product from steam-hydrocarbon reformers used in the productionofammonia, gasoline, and other chemicals; other sources include fermentation, deep gas wells,

and direct production from carbonaceous fuels. Whatever the source, the crude CO2 (containingat least 90% CO2) is compressed in either two or three stages, cooled, purified, condensed to the

liquid phase, and placed in insulated storage vessels. Carbon dioxide is distributed in three ways;in high-pressure uninsulated steel cylinders; as a low-pressure liquid in insulated truck trailers or

rail tank cars; and as dry ice in insulated boxes, trucks, or boxcars.

World of the Body: carbon dioxide

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When the body burns food the end products are mainly water and carbon dioxide, together withsome nitrogenous chemicals such as urea. The carbon dioxide enters the bloodstream, is carried

to the lungs, and is excreted in the expired air ofbreathing. The atmospheric air we inhale

contains virtually no carbon dioxide, whereas there is about 5% in the air we breathe out.

Carbon dioxide reacts in the blood to form carbonic acid and bicarbonate and, if it were allowed

to accumulate, would cause acidosis. This condition is particularly harmful to the cells of the

brain. Carbon dioxide diffuses into the liquid in the brain, thecerebrospinal fluid (CSF) ; any

excess makes it more acid, and this in turn stimulates neural receptors in thebrain stem thatincrease breathing. The result is that the carbon dioxide is blown off in the lungs and the acidity

of the blood and brain are kept close to normal levels. Carbon dioxide is the main chemicalstimulus to breathing, which is regulated primarily to keep blood and brain acidity at healthy

values. If the carbon dioxide in the lungs increases by only 0.2%, from a normal level of about

5%, then breathing is doubled. Breathholding accumulates carbon dioxide in the body, which

leads to an irrepressible desire to breathe (lack of oxygen is also a stimulus, but far weaker thancarbon dioxide). Conversely, if we voluntarily hyperventilate, the level of carbon dioxide in the

blood will decrease, and breathing may be inhibited until more carbon dioxide accumulates.

Hyperventilationcan have harmful effects because of the pronounced reduction in blood andCSF acidity. Since decreases in carbon dioxide and acidity constrictblood vessels, particularly in

the brain, one effect is to reduce the blood supply to the brain.

Carbon dioxide was identified, but not understood chemically, in about 1600 AD by van Helmont,

who called it gas sylvestre, the gas produced by combustion. He showed that it would not

support life. Later Joseph Black, who had a lifelong interest in chemistry and was Professor ofMedicine in Glasgow from 1757 to 1766, called it fixed acid, because it was absorbed by lime

solution, and he showed that it was produced in respiration. The story goes that in 1764 Black

climbed to the ceiling of a church in Glasgow, occupied for 10 hours of religious devotions by a
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congregation of 1500, and measured the fixed acid that was exhaled by the diligent and sleepy

congregation. But it was Lavoisier (1743-94) who definitely established the excretion of carbon

dioxide after its formation in metabolism, although he erroneously believed that it was formed inthe lungs. Lavoisier was guillotined, and it was said that it took but a second to cut off his head;

a hundred years will not suffice to produce one like it. Lavoisier concluded that any series of

lectures in an auditorium extending over 3 hours would leave the audience in a soporific statedue to the accumulation of carbon dioxide. In theory he was right. Carbon dioxide in excess can

act as an anaesthetic and, in animals, major surgery has been performed under its influence

alone. Some human lung diseases such as chronic bronchitis may leave the patient drowsy oreven comatose because of the build up of carbon dioxide in the body. It is claimed, probably

incorrectly, that in social environments yawning and weariness are due to an accumulation of

carbon dioxide. Van Helmont investigated a Grotto del Cane (cave of dogs) in Italy in which it

was claimed, rather implausibly, that a tall dog owner would survive while his lowly dog wouldperish, due to the depressant effect of carbon dioxide, held to the ground because of its greater

density than air. Perhaps Black's Glasgow congregation was fortunate.

John Widdicombe

See also acid-base homeostasis;blood; respiration.

Dental Dictionary: carbon dioxide

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Home > Library > Health >Dental Dictionary

n

A colorless, odorless gas produced by the complete oxidation of carbon. Carbon dioxide is aproduct of cell respiration and is carried by the blood to the lungs and exhaled. The acid-basebalance of body fluids and tissues is affected by the level of carbon dioxide and its carbonate

compounds.

Britannica Concise Encyclopedia: carbon dioxide

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Home > Library > Miscellaneous> Britannica Concise Encyclopedia

Inorganic compound, a colourless gas with a faint, sharp odour and a sour taste when dissolved

in water, chemical formula CO2. Constituting about 0.03% of air by volume, it is produced whencarbon-containing materials burn completely, and it is a product offermentation and animal

respiration. Plants use CO2 inphotosynthesis to make carbohydrates. CO2 in Earth's atmospherekeeps some of the Sun's energy from radiating back into space (seegreenhouse effect). In water,

CO2 forms a solution of a weakacid, carbonic acid (H2CO3). The reaction of CO2 and ammonia

is the first step in synthesizing urea. An important industrial material, CO2 is recovered fromsources including flue gases, limekilns, and the process that prepares hydrogen for synthesis of

ammonia. It is used as a refrigerant, a chemical intermediate, and an inert atmosphere; in fire
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extinguishers, foam rubber and plastics, carbonated beverages (seecarbonation), and aerosol

sprays; in water treatment, welding, and cloud seeding; and for promoting plant growth in

greenhouses. Under pressure it becomes a liquid, the form most often used in industry. If theliquid is allowed to expand, it cools and partially freezes to the solid form, dry ice.

For more information on carbon dioxide, visitBritannica.com.

Sports Science and Medicine: carbon dioxide

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Home > Library > Health >Sports Science and Medicine

A colourless gas which makes up about 0.04% of the atmosphere. It is denser than air. It is toxic

only above about 6% concentration, but it does not support respiration or combustion. It isexcreted as a waste product ofaerobic metabolism, and is carried to the veins, mainly as

hydrogen carbonate (bicarbonate) ions. Expired air contains about 4% carbon dioxide. Increases

in carbon dioxide levels stimulate thevasomotorcentre to increase the ventilation rate so thatmore carbon dioxide can be eliminated from the lungs.

Columbia Encyclopedia: carbon dioxide

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Home > Library > Miscellaneous> Columbia Encyclopediacarbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one

and one-half times as dense as air under ordinary conditions of temperature and pressure. It does

not burn, and under normal conditions it is stable, inert and nontoxic. It will however supportcombustion of magnesium to give magnesium oxide and carbon. Although it is not a poison, it

can cause death by suffocation if inhaled in large amounts. It is a fairly stable compound butdecomposes at very high temperatures into carbon and oxygen. It is fairly soluble in water, onevolume of it dissolving in an equal volume of water at room temperature and pressure; the

resultant weakly acidic aqueous solution is called carbonic acid. The gas is easily liquefied by

compression and cooling. If liquid carbon dioxide is quickly decompressed it rapidly expands

and some of it evaporates, removing enough heat so that the rest of it cools into solid carbondioxide "snow." A standard test for the presence of carbon dioxide is its reaction with limewater

(a saturated water solution ofcalcium hydroxide) to form a milky-white precipitate of calcium

hydroxide.

Carbon dioxide occurs in nature both free and in combination (e.g., in carbonates). It is part of

the atmosphere, making up about 1% of the volume of dry air. Because it is a product ofcombustion of carbonaceous fuels (e.g., coal, coke, fuel oil, gasoline, and cooking gas), there is

usually more of it in city air than in country air. The natural balance of carbon dioxide in theatmosphere is growing from its stable level of 0.13% to a predicted 0.14% by the year 2000. It is

anticipated that this extra carbon dioxide will fuel the greenhouse effect, warm the atmosphere,

and further disrupt the natural carbon dioxide cycle (seeglobal warming).
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In various parts of the world-notably in Italy, Java, and Yellowstone National Park in the United

States-carbon dioxide is formed underground and issues from fissures in the earth. Natural

mineral waters such as Vichy water sparkle (effervesce) because excess carbon dioxide thatdissolved in them under pressure collects in bubbles and escapes when the pressure is released.

The chokedamp (see damp) of mines, pits, and old, unused wells is largely carbon dioxide.

Carbon dioxide is a raw material forphotosynthesisin green plants and is a product of animalrespiration. It is also a product of the decay of organic matter.

Carbon dioxide has varied commercial uses. Its greatest use as a chemical is in the production of

carbonated beverages; it provides the sparkle in carbonated beverages such as soda water.

Formed by the action of yeast or baking powder, carbon dioxide causes the rising of breaddough. The compound is also used in water softening, in the manufacture of aspirin and lead

paint pigments, and in the Solvay process for the preparation of sodium carbonate. In some fire

extinguishers carbon dioxide is expelled through a nozzle and settles on the flame, smothering it.It also has numerous nonchemical uses. It is used as a pressurizing medium and propellant, e.g.,

in aerosol cans of food, in fire extinguishers, in target pistols, and for inflating life rafts. Because

it is relatively inert, it is used to provide a nonreactive atmosphere, e.g., for packaging foods,such as coffee, that can be spoiled by oxidation during storage. Solid carbon dioxide, known asdry ice, is used as a refrigerating agent.

There are three principal commercial sources for carbon dioxide. High-purity carbon dioxide is

produced from some wells. The gas is obtained as a byproduct of chemical manufacture, as in thefermentation of grain to make alcohol and the burning of limestone to make lime. It is also

manufactured directly by burning carbonaceous fuels. For commercial use it is available as a

liquid under high pressure in steel cylinders, as a low-temperature liquid at lower pressures, and

as the solid dry ice.

Wine Lover's Companion:carbon dioxideTop

Home > Library > Food & Cooking> Wine Lover's Companion

A colorless, odorless, incombustible gas. Carbon dioxide (CO2) is one of the two by-products ofFERMENTATION, the other beingALCOHOL. Yeast acts on the natural grape sugar and converts 40 to

45 percent of it to carbon dioxide, which in most cases escapes into the air. In the production ofSPARKLINGWINES, however, carbon dioxide is purposely trapped in the wine to create

effervescence.

Science Dictionary: carbon dioxideTop

Home > Library > Science> Science Dictionary

A compound made up ofmolecules containing one carbonatom and two oxygenatoms.
http://www.answers.com/topic/damphttp://www.answers.com/topic/photosynthesishttp://www.answers.com/topic/photosynthesishttp://www.answers.com/topic/respirationhttp://www.answers.com/topic/respirationhttp://www.answers.com/topic/solvay-processhttp://www.answers.com/library/Wine%20Lover's%20Companion-cid-12941http://www.answers.com/library/Wine%20Lover's%20Companion-cid-12941http://www.answers.com/http://www.answers.com/main/what_content.jsphttp://www.answers.com/main/food.jsphttp://www.answers.com/main/food.jsphttp://www.answers.com/library/Wine+Lover's+Companion-cid-12941http://www.answers.com/topic/alcoholhttp://www.answers.com/topic/alcoholhttp://www.answers.com/topic/alcoholhttp://www.answers.com/topic/alcoholhttp://www.answers.com/topic/sparkling-winehttp://www.answers.com/topic/sparkling-winehttp://www.answers.com/topic/sparkling-winehttp://www.answers.com/topic/sparkling-winehttp://www.answers.com/library/Science%20Dictionary-cid-12941http://www.answers.com/http://www.answers.com/main/what_content.jsphttp://www.answers.com/main/science.jsphttp://www.answers.com/main/science.jsphttp://www.answers.com/library/Science+Dictionary-cid-12941http://www.answers.com/topic/moleculehttp://www.answers.com/topic/carbonhttp://www.answers.com/topic/atomhttp://www.answers.com/topic/atomhttp://www.answers.com/topic/oxygenhttp://www.answers.com/topic/oxygenhttp://www.answers.com/topic/damphttp://www.answers.com/topic/photosynthesishttp://www.answers.com/topic/respirationhttp://www.answers.com/topic/solvay-processhttp://www.answers.com/library/Wine%20Lover's%20Companion-cid-12941http://www.answers.com/http://www.answers.com/main/what_content.jsphttp://www.answers.com/main/food.jsphttp://www.answers.com/library/Wine+Lover's+Companion-cid-12941http://www.answers.com/topic/alcoholhttp://www.answers.com/topic/sparkling-winehttp://www.answers.com/library/Science%20Dictionary-cid-12941http://www.answers.com/http://www.answers.com/main/what_content.jsphttp://www.answers.com/main/science.jsphttp://www.answers.com/library/Science+Dictionary-cid-12941http://www.answers.com/topic/moleculehttp://www.answers.com/topic/carbonhttp://www.answers.com/topic/atomhttp://www.answers.com/topic/oxygen


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Carbon dioxide is normally found as a gas that is breathed out by animals and absorbed by

green plants. The plants, in turn, return oxygento the atmosphere. (Seecarbon cycleand

respiration.)Carbon dioxide is also given off in the burning of fossil fuels ( seegreenhouse effect).

Veterinary Dictionary: carbon dioxide

Top

Home > Library > Animal Life >Veterinary Dictionary

An odorless, colorless gas, CO2, resulting from oxidation of carbons, formed in the tissues and

eliminated by the lungs; used with oxygen to stimulate respiration and in solid form (carbondioxide snowsee below) as an escharotic, as a gas to euthanize laboratory rabbits and rodents.

c. d. anesthesia exposure of pigs for 45 seconds in a mixture of 60 to 70% CO2 in air is

an adequate pre-slaughter anesthetic for pigs.

c. d. combining power the ability of blood plasma to combine with carbon dioxide;

indicative of the alkali reserve and a measure of the acidbase balance of the blood. c. d. content the amount of carbonic acid and bicarbonate in the blood; reported in

millimoles per liter.

c. d. dissociation curve a graph demonstrating the relationship between the blood

content of CO2 and thePco2.

c. d. narcosis respiratory acidosis.

c. d. snow solid carbon dioxide, formed by rapid evaporation of liquid carbon dioxide;it gives a temperature of about 110F (79C), and is used as an escharotic in various

skin diseases. Called also dry ice.

c. d. tension the partial pressure of carbon dioxide in the blood; noted asPco2 inbloodgas analysis. See also respiration.

c. d. transport carbon dioxide passes from tissues to blood by diffusion, in the bloodby solution and via reactions within plasma and erythrocytes, from blood to pulmonaryalveoli by diffusion.

Cosmic Lexicon: Carbon dioxide

Top

Home > Library > Science> Cosmic Lexicon

A compound formed by combining one carbon atom with two oxygen atoms, making the

molecule CO2. Carbon dioxide is an important part of the atmospheres of Venus and Mars.

Carbon dioxide gas condenses to a solid below -78o

C. This solid is commonly known as dry ice.The polar ice caps on Mars are made of frozen water and carbon dioxide.

Wikipedia: Carbon dioxide

Top

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"CO2" redirects here. For the postal district, see CO postcode area.

Carbon dioxide

IUPAC name

Carbon dioxide

Other namesCarbonic acid gas; carbonic

anhydride;dry ice (solid)

Identifiers

CAS number 124-38-9

PubChem 280

EC number 204-696-9

UN number

1013

Solid (dry ice):1845

Mixtures withEthylene oxide:1952,3300

RTECS number FF6400000

SMILES

C(=O)=O

InChI1/CO2/c2-1-3

ChemSpiderID 274

Properties

Molecular formula CO2

Molar mass 44.010 g mol-1

Appearance colorless, odorless gas

Density

1.562 g mL-1(solid at 1 atm and 78.5 C)

0.770 g mL-1(liquid at 56 atm and 20 C)

1.97

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