Difference between revisions of "Chemical reaction" - New World Encyclopedia

Revision as of 23:06, 29 August 2008

For other uses, see Chemical reaction (disambiguation).

Vapors of hydrogen chloride in a beaker and ammonia in a test tube meet to form a cloud of a new substance, ammonium chloride

A chemical reaction is a process that always results in the interconversion of chemical substances.^[1] The substance or substances initially involved in a chemical reaction are called reactants. Chemical reactions are usually characterized by a chemical change, and they yield one or more products which are, in general, different from the reactants. Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical equation, is applicable to transformations of elementary particles, as well as nuclear reactions.

Different chemical reactions are used in combinations in chemical synthesis in order to get a desired product. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, by which syntheses and decompositions ordinarily impossible in conditions within a cell are performed.

Reaction types

The large diversity of chemical reactions and approaches to their study results in the existence of several concurring, often overlapping, ways of classifying them. Below are examples of widely used terms for describing common kinds of reactions.

Isomerisation, in which a chemical compound undergoes a structural rearrangement without any change in its net atomic composition; see stereoisomerism
Direct combination or synthesis, in which 2 or more chemical elements or compounds unite to form a more complex product:

N₂ + 3 H₂ → 2 NH₃

Chemical decomposition or analysis, in which a compound is decomposed into smaller compounds or elements:

2 H₂O → 2 H₂ + O₂

Single displacement or substitution, characterized by an element being displaced out of a compound by a more reactive element:

2 Na(s) + 2 HCl(aq) → 2 NaCl(aq) + H₂(g)

Metathesis or Double displacement reaction, in which two compounds exchange ions or bonds to form different compounds:

NaCl(aq) + AgNO₃(aq) → NaNO₃(aq) + AgCl(s)

Acid-base reactions, broadly characterized as reactions between an acid and a base, can have different definitions depending on the acid-base concept employed. Some of the most common are:

Arrhenius definition: Acids dissociate in water releasing H₃O⁺ ions; bases dissociate in water releasing OH^- ions.
Brønsted-Lowry definition: Acids are proton (H⁺) donors; bases are proton acceptors. Includes the Arrhenius definition.
Lewis definition: Acids are electron-pair acceptors; bases are electron-pair donors. Includes the Brønsted-Lowry definition.

Redox reactions, in which changes in oxidation numbers of atoms in involved species occur. Those reactions can often be interpreted as transferences of electrons between different molecular sites or species. A typical example of redox rection is:

2 S₂O₃²⁻(aq) + I₂(aq) → S₄O₆²⁻(aq) + 2 I⁻(aq)

In which I₂ is reduced to I^- and S₂O₃^2- (thiosulfate anion) is oxidized to S₄O₆^2-.

Combustion, a kind of redox reaction in which any combustible substance combines with an oxidizing element, usually oxygen, to generate heat and form oxidized products. The term combustion is usually used for only large-scale oxidation of whole molecules, i.e. a controlled oxidation of a single functional group is not combustion.

C₁₀H₈+ 12 O₂ → 10 CO₂ + 4 H₂O

CH₂S + 6 F₂ → CF₄ + 2 HF + SF₆

Organic reactions encompass a wide assortment of reactions involving compounds which have carbon as the main element in their molecular structure. The reactions in which an organic compound may take part are largely defined by its functional groups. Defined in opposition to inorganic reactions. Reactions can also be classified according to their mechanism, some typical examples being:

Reactions of ions, e.g. disproportionation of hypochlorite
Reactions with reactive ionic intermediates, e.g. reactions of enolates
Radical reactions, e.g. combustion at high temperature
Reactions of carbenes

Chemical kinetics

The rate of a chemical reaction is a measure of how the concentration or pressure of the involved substances changes with time. Analysis of reaction rates is important for several applications, such as in chemical engineering or in chemical equilibrium study. Rates of reaction depends basically on:

Reactant concentrations, which usually make the reaction happen at a faster rate if raised through increased collisions per unit time,
Surface area available for contact between the reactants, in particular solid ones in heterogeneous systems. Larger surface area leads to higher reaction rates.
Pressure, by increasing the pressure, you decrease the volume between molecules. This will increase the frequency of collisions of molecules.
Activation energy, which is defined as the amount of energy required to make the reaction start and carry on spontaneously. Higher activation energy implies that the reactants need more energy to start than a reaction with a lower activation energy.
Temperature, which hastens reactions if raised, since higher temperature increases the energy of the molecules, creating more collisions per unit time,
The presence or absence of a catalyst. Catalysts are substances which change the pathway (mechanism) of a reaction which in turn increases the speed of a reaction by lowering the activation energy needed for the reaction to take place. A catalyst is not destroyed or changed during a reaction, so it can be used again.
For some reactions, the presence of electromagnetic radiation, most notably ultra violet, is needed to promote the breaking of bonds to start the reaction. This is particularly true for reactions involving radicals.

Reaction rates are related to the concentrations of substances involved in reactions, as quantified by the rate law of each reaction. Note that some reactions have rates that are independent of reactant concentrations. These are called zero order reactions.

References
ISBN links support NWE through referral fees

↑ International Union of Pure and Applied Chemistry. "chemical reaction". Compendium of Chemical Terminology Internet edition.

ar:تفاعل كيميائي be:Хімічная рэакцыя bs:Hemijska reakcija bg:Химична реакция ca:Reacció química cs:Chemická reakce da:Kemisk reaktion de:Chemische Reaktion et:Keemiline reaktsioon el:Χημική αντίδραση es:Reacción química eo:Kemia reakcio fa:واکنش شیمیایی fr:Réaction chimique gl:Reacción química hi:रासायनिक अभिक्रिया ko:화학 반응 hr:Kemijska reakcija io:Kemiala reakto id:Reaksi kimia is:Efnahvarf it:Reazione chimica he:תגובה כימית lv:Ķīmiskā reakcija lt:Cheminė reakcija lmo:Reassiun chimiga hu:Kémiai reakció mk:Хемиска реакција ms:Tindak balas kimia nl:Chemische reactie ja:化学反応 no:Kjemisk reaksjon nn:Kjemisk reaksjon nds:Cheemsch Reakschoon pl:Reakcja chemiczna pt:Reacção química ru:Химические реакции sq:Reaksioni kimik simple:Chemical reaction sk:Chemická reakcia sl:Kemična sprememba sr:Хемијска реакција sh:Hemijska reakcija su:Réaksi kimiawi fi:Kemiallinen reaktio sv:Kemisk reaktion tl:Reaksyong kimikal ta:வேதியியற் தாக்கம் th:ปฏิกิริยาเคมี vi:Phản ứng hóa học tr:Kimyasal tepkime uk:Хімічна реакція ur:کیمیائی تعامل zh-yue:化學反應 zh:化学反应

[1] International Union of Pure and Applied Chemistry. "chemical reaction". Compendium of Chemical Terminology Internet edition.

[1]

@@ Line 1: / Line 1: @@
+{{otheruses}}
-[[Image:Hydrochloric acid ammonia.jpg|right|180px|thumb|Vapors of [[hydrogen chloride]] in a beaker and [[ammonia]] in a test tube meet to form a cloud of a new substance, [[ammonium chloride]].]]
+[[Image:Hydrochloric acid ammonia.jpg|right|180px|thumb|Vapors of [[hydrogen chloride]] in a beaker and [[ammonia]] in a test tube meet to form a cloud of a new substance, [[ammonium chloride]]]]
+A '''chemical reaction''' is a process that always results in the interconversion of [[chemical substance]]s.<ref>{{GoldBookRef|title=chemical reaction|file=C01033}}</ref> The substance or substances initially involved in a chemical reaction are called [[reactants]]. Chemical reactions are usually characterized by a [[chemical change]], and they yield one or more [[Product (chemistry)|products]] which are, in general, different from the reactants. Classically, chemical reactions encompass changes that strictly involve the motion of [[electrons]] in the forming and breaking of [[chemical bond]]s, although the general concept of a chemical reaction, in particular the notion of a [[chemical equation]], is applicable to [[Feynman diagram|transformations of elementary particles]], as well as [[nuclear reaction]]s.
-A '''chemical reaction''' is a process that results in the interconversion of [[chemical substance]]s.<ref>{{GoldBookRef|title=chemical reaction|file=C01033}}</ref> The substance or substances initially involved in a chemical reaction are called [[reactants]]. Chemical reactions are usually characterized by a [[chemical change]], and they yield one or more [[Product (chemistry)|products]] which are, in general, different from the reactants. Classically, chemical reactions encompass changes that strictly involve the motion of [[electrons]] in the forming and breaking of [[chemical bond]]s, although the general concept of a chemical reaction, in particular the notion of a [[chemical equation]], is applicable to [[Feynman diagram|transformations of elementary particles]], as well as [[nuclear reaction]]s.
 Different chemical reactions are used in combinations in [[chemical synthesis]] in order to get a desired product. In [[biochemistry]], series of chemical reactions [[catalysis|catalyzed]] by [[enzymes]] form [[metabolic pathways]], by which syntheses and decompositions ordinarily impossible  in conditions within a cell are performed.
 == Reaction types ==
+[[list of reactions|The large diversity of chemical reactions]] and approaches to their study results in the existence of several concurring, often overlapping, ways of classifying them. Below are examples of widely used terms for describing common kinds of reactions.
-[[list of reactions|The large diversity of chemical reactions]] and of approaches to their study results in the existence of several concurring, often overlapping, ways of classifying them. Below are examples of widely used terms for describing common kinds of reactions:
+*[[Isomerisation]], in which a chemical compound undergoes a structural rearrangement without any change in its net atomic composition; see [[stereoisomerism]]
+*[[Combination reaction|Direct combination]] or [[Chemical synthesis|synthesis]], in which 2 or more chemical elements or compounds unite to form a more complex product:
-*[[Isomerisation]], in which a chemical compound undergoes a structural rearrangement without any change in its net atomic composition.
-*[[Combination reaction|Direct combination]] or [[Chemical synthesis|synthesis]], in which two or more chemical elements or compounds unite to form a more complex product:
 ::[[Nitrogen|N]]<sub>2</sub> + 3 [[Hydrogen|H]]<sub>2</sub> → 2 [[Ammonia|NH<sub>3]]</sub>
 *[[Chemical decomposition]] or '''analysis''', in which a compound is decomposed into smaller compounds or elements:
 ::2 [[Water|H<sub>2</sub>O]] → 2 H<sub>2</sub> + [[Oxygen|O]]<sub>2</sub>
 *[[Single displacement reaction|Single displacement]] or [[substitution (chemistry)|substitution]], characterized by an element being displaced out of a compound by a more [[Reactivity series|reactive]] element:
-::2 [[Sodium|Na]](s) + 2 [[Hydrogen chloride|HCl]](aq) → 2 [[Sodium chloride|NaCl]](aq) + H<sub>2</sub>(g)
+::2 [[Sodium|Na]](s) + 2 [[Hydrogen chloride|HCl]][[(aq)]] → 2 [[Sodium chloride|NaCl]](aq) + H<sub>2</sub>(g)
 *[[Metathesis reaction (chemistry)|Metathesis]] or '''Double displacement reaction''', in which two compounds exchange [[ion]]s or bonds to form different compounds:
 ::NaCl(aq) + [[Silver nitrate|AgNO<sub>3</sub>]](aq) → [[Sodium nitrate|NaNO<sub>3</sub>]](aq) + [[Silver chloride|AgCl]](s)
-*[[Precipitation]] Reactions where species in solution combine to form a solid product (precipitate). A typical example would be the reaction of methatesis described above.
+*[[Acid-base]] reactions, broadly characterized as reactions between an [[acid]] and a [[Base (chemistry)|base]], can have different definitions depending on the acid-base concept employed. Some of the most common are:
-*[[Acid-base]] reactions, broadly characterized as reactions betwwen an [[acid]] and a [[base]], can have different definitions depending on the acid-base concept employed. Some of the most common are:
 :* [[Acid-base#The Arrhenius definition|Arrhenius]] definition: Acids dissociate in water releasing H<sub>3</sub>O<sup>+</sup> ions; bases dissociate in water releasing OH<sup>-</sup> ions.
 :* [[Brønsted-Lowry acid-base theory|Brønsted-Lowry]] definition: Acids are proton (H<sup>+</sup>) donors; bases are proton acceptors. Includes the Arrhenius definition.
-:* [[Acid-base#The Lewis definition|Lewis]] definiton: Acids are electron-pair acceptors; bases are electron-pair donors. Includes the Brønsted-Lowry definition.
+:* [[Acid-base#The Lewis definition|Lewis]] definition: Acids are electron-pair acceptors; bases are electron-pair donors. Includes the Brønsted-Lowry definition.
-* [[Redox reaction]]s, in which changes in [[oxidation number]]s of atoms in involved species occur. Those reactions can often be interpreted as the transfer of electrons between different molecular sites or species. A typical example of a redox rection is:
+* [[Redox reaction]]s, in which changes in [[oxidation number]]s of atoms in involved species occur. Those reactions can often be interpreted as transferences of electrons between different molecular sites or species. A typical example of redox rection is:
 :2 S<sub>2</sub>O<sub>3</sub><sup>2−</sup>(aq) + I<sub>2</sub>(aq) → S<sub>4</sub>O<sub>6</sub><sup>2−</sup>(aq) + 2 I<sup>−</sup>(aq)
-In this reaction, I<sub>2</sub> is reduced to I<sup>-</sup> and S<sub>2</sub>O<sub>3</sub><sup>2-</sup> ([[thiosulfate]] anion) is oxidized to S<sub>4</sub>O<sub>6</sub><sup>2-</sup>.
+In which I<sub>2</sub> is reduced to I<sup>-</sup> and S<sub>2</sub>O<sub>3</sub><sup>2-</sup> ([[thiosulfate]] anion) is oxidized to S<sub>4</sub>O<sub>6</sub><sup>2-</sup>.
-:*[[Combustion]], a kind of redox reaction in which any combustible substance combines with an oxidizing element, usually oxygen, to generate heat and form oxidized products. The term combustion is used usually only large-scale oxidation of whole molecules, i.e. a controlled oxidation of a single functional group is not combustion.
+*[[Combustion]], a kind of redox reaction in which any combustible substance combines with an oxidizing element, usually oxygen, to generate heat and form oxidized products. The term combustion is usually used for only large-scale oxidation of whole molecules, i.e. a controlled oxidation of a single functional group is not combustion.
 ::C<sub>10</sub>H<sub>8</sub>+ 12 O<sub>2</sub> → 10 CO<sub>2</sub> + 4 H<sub>2</sub>O
 ::CH<sub>2</sub>S + 6 [[fluorine|F<sub>2</sub>]] → [[carbon tetrafluoride|CF<sub>4</sub>]] + 2 [[hydrogen fluoride|HF]] + [[sulfur hexafluoride|SF<sub>6</sub>]]
-* [[Organic reaction]]s encompass a wide assortment of reactions involving [[Organic compound|compounds]] which have [[carbon]] as the main element in their molecular structure. The reactions an organic compound may take part are largely defined by its [[functional group]]s. Defined in opposition to [[Inorganic chemical reaction|inorganic reactions]].
+[[Organic reaction]]s encompass a wide assortment of reactions involving [[Organic compound|compounds]] which have [[carbon]] as the main element in their molecular structure. The reactions in which an organic compound may take part are largely defined by its [[functional group]]s. Defined in opposition to [[Inorganic chemical reaction|inorganic reactions]].
 Reactions can also be classified according to their mechanism, some typical examples being:
-*Reactions of ions, e.g. [[disproportionation]] of [[hypochlorite]]
+:*Reactions of ions, e.g. [[disproportionation]] of [[hypochlorite]]
-*Reactions with reactive ionic intermediates, e.g. reactions of [[enolate]]s
+:*Reactions with reactive ionic intermediates, e.g. reactions of [[enolate]]s
-*[[Radical (chemistry)|Radical]] reactions, e.g. combustion at high temperature
+:*[[Radical (chemistry)|Radical]] reactions, e.g. combustion at high temperature
-*Reactions of [[carbene]]s
+:*Reactions of [[carbene]]s
-Some branches of chemistry include any detectable changes in [[chemical conformation]] in the reaction types, while others consider these changes merely as physical properties of a compound.
-The collision of more than two particles into the ordered structure necessary to perform chemical transformations is extremely unlikely; which is why ternary reactions in practice are not observed. A chemical reaction may require three or more reagents, but the process can generally be best described as a [[stepwise reaction|stepwise]] series of [[elementary reaction]]s.
 == Chemical kinetics ==
@@ Line 47: / Line 39: @@
 The [[reaction rate|rate]] of a chemical reaction is a measure of how the [[concentration]] or [[pressure]] of the involved substances changes with time. Analysis of reaction rates is important for several applications, such as in [[chemical engineering]] or in [[chemical equilibrium]] study. Rates of reaction depends basically on:
 *[[Reactant]] concentrations, which usually make the reaction happen at a faster rate if raised through increased collisions per unit time,
-*[[Surface area]], the amount of the substance being used,
+*[[Surface area]] available for contact between the reactants, in particular solid ones in heterogeneous systems. Larger surface area leads to higher reaction rates.
 *[[Pressure]], by increasing the pressure, you decrease the volume between molecules.  This will increase the frequency of collisions of molecules.
 *[[Activation energy]], which is defined as the amount of energy required to make the reaction start and carry on spontaneously. Higher activation energy implies that the reactants need more energy to start than a reaction with a lower activation energy.
@@ Line 57: / Line 49: @@
 ==See also==
+*[[List of reactions]]
-* [[Acid]]
+*[[Organic reaction]]
-* [[Base (chemistry)]]
+*[[Inorganic chemical reaction]]
-* [[Catalyst]]
+*[[List of important publications in chemistry]]
-* [[Chemical bond]]
+*[[Stoichiometry]]
-* [[Chemical equation]]
+*[[Stoichiometric coefficient]]
-* [[Combustion]]
+*[[Transition state theory]]
-* [[Redox]]
+*[[Gas stoichiometry]]
+*[[Thermodynamic databases for pure substances]]
-== Notes ==
+*[[Autocatalytic reaction]]
-<references/>
+*[[Coefficients]]
 == References ==
+{{reflist}}
-* Chang, Raymond. 2006. ''Chemistry''. 9th ed. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031.
+[[Category:Chemical reactions]]
-* Cotton, F. Albert, and Geoffrey Wilkinson. 1980. ''Advanced Inorganic Chemistry''. 4th ed. New York: Wiley. ISBN 0471027758.
-* McMurry, J., and R.C. Fay. 2004. ''Chemistry''. 4th ed. Upper Saddle River, NJ: Prentice Hall. ISBN 0131402080.
-[[Category:Physical sciences]]
 [[Category:Chemistry]]
-{{credit|165126019}}
+[[ar:تفاعل كيميائي]]
+[[be:Хімічная рэакцыя]]
+[[bs:Hemijska reakcija]]
+[[bg:Химична реакция]]
+[[ca:Reacció química]]
+[[cs:Chemická reakce]]
+[[da:Kemisk reaktion]]
+[[de:Chemische Reaktion]]
+[[et:Keemiline reaktsioon]]
+[[el:Χημική αντίδραση]]
+[[es:Reacción química]]
+[[eo:Kemia reakcio]]
+[[fa:واکنش شیمیایی]]
+[[fr:Réaction chimique]]
+[[gl:Reacción química]]
+[[hi:रासायनिक अभिक्रिया]]
+[[ko:화학 반응]]
+[[hr:Kemijska reakcija]]
+[[io:Kemiala reakto]]
+[[id:Reaksi kimia]]
+[[is:Efnahvarf]]
+[[it:Reazione chimica]]
+[[he:תגובה כימית]]
+[[lv:Ķīmiskā reakcija]]
+[[lt:Cheminė reakcija]]
+[[lmo:Reassiun chimiga]]
+[[hu:Kémiai reakció]]
+[[mk:Хемиска реакција]]
+[[ms:Tindak balas kimia]]
+[[nl:Chemische reactie]]
+[[ja:化学反応]]
+[[no:Kjemisk reaksjon]]
+[[nn:Kjemisk reaksjon]]
+[[nds:Cheemsch Reakschoon]]
+[[pl:Reakcja chemiczna]]
+[[pt:Reacção química]]
+[[ru:Химические реакции]]
+[[sq:Reaksioni kimik]]
+[[simple:Chemical reaction]]
+[[sk:Chemická reakcia]]
+[[sl:Kemična sprememba]]
+[[sr:Хемијска реакција]]
+[[sh:Hemijska reakcija]]
+[[su:Réaksi kimiawi]]
+[[fi:Kemiallinen reaktio]]
+[[sv:Kemisk reaktion]]
+[[tl:Reaksyong kimikal]]
+[[ta:வேதியியற் தாக்கம்]]
+[[th:ปฏิกิริยาเคมี]]
+[[vi:Phản ứng hóa học]]
+[[tr:Kimyasal tepkime]]
+[[uk:Хімічна реакція]]
+[[ur:کیمیائی تعامل]]
+[[zh-yue:化學反應]]
+[[zh:化学反应]]

Difference between revisions of "Chemical reaction" - New World Encyclopedia

Revision as of 23:06, 29 August 2008

Reaction types

Chemical kinetics

See also

ReferencesISBN links support NWE through referral fees

References
ISBN links support NWE through referral fees