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A chemical reaction is a process that always results in the interconversion of chemical substance
Chemical substance

A chemical substance is a material with a specific Empirical formula. It is a concept that became firmly established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate....
s. The substance or substances initially involved in a chemical reaction are called reactants. Chemical reactions are usually characterized by a chemical change
Chemical change

In a chemical reaction, chemical bonds are broken and new bonds are formed between different atoms. This breaking and forming of bonds takes place when particles of the original materials collide with one another....
, and they yield one or more products
Product (chemistry)

A product is a substance that forms as a result of a biological- or chemical reaction. While the end product of some chemical reactions may be the result of a relatively rapid reaction, nanoseconds to seconds, chemical equilibrium in complex systems may require years or even centuries to be established....
, which usually have properties different from the reactants.






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Hydrochloric Acid Ammonia
A chemical reaction is a process that always results in the interconversion of chemical substance
Chemical substance

A chemical substance is a material with a specific Empirical formula. It is a concept that became firmly established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate....
s. The substance or substances initially involved in a chemical reaction are called reactants. Chemical reactions are usually characterized by a chemical change
Chemical change

In a chemical reaction, chemical bonds are broken and new bonds are formed between different atoms. This breaking and forming of bonds takes place when particles of the original materials collide with one another....
, and they yield one or more products
Product (chemistry)

A product is a substance that forms as a result of a biological- or chemical reaction. While the end product of some chemical reactions may be the result of a relatively rapid reaction, nanoseconds to seconds, chemical equilibrium in complex systems may require years or even centuries to be established....
, which usually have properties different from the reactants. Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bond
Chemical bond

A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds....
s, although the general concept of a chemical reaction, in particular the notion of a chemical equation
Chemical equation

A chemical equation may be described as a chemical reaction or a means of writing out and describing such a phenomenon. The coefficients next to the symbols and formulae of entities are the absolute values of the stoichiometric coefficient....
, is applicable to transformations of elementary particles
Feynman diagram

In quantum field theory a Feynman diagram is an intuitive graphical representation of a contribution to the transition amplitude or correlation function of a quantum mechanical or statistical field theory....
, as well as nuclear reaction
Nuclear reaction

In nuclear physics, a nuclear reaction is the process in which two atomic nucleus or subatomic particles collide to produce products different from the initial particles....
s.

Different chemical reactions are used in combination in chemical synthesis
Chemical synthesis

In chemistry, chemical synthesis is purposeful execution of chemical reactions in order to get a product , or several products. This happens by physics and chemical manipulations usually involving one or more reactions....
 in order to get a desired product. In biochemistry
Biochemistry

Biochemistry is the study of the chemistry processes in living organisms. It deals with the structure and function of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules....
, series of chemical reactions catalyzed
Catalysis

Catalysis is the process in which the reaction rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst....
 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
    Isomerisation

    In chemistry isomerisation is the process by which one molecule is transformed into another molecule which has exactly the same atoms, but the atoms are rearranged e.g....
    , in which a chemical compound undergoes a structural rearrangement without any change in its net atomic composition; see stereoisomerism
    Stereoisomerism

    Stereoisomers are isomer that have the same molecular formula and sequence of bonded atoms , but which differ in the three dimensional orientations of their atoms in space....
  • Direct combination
    Combination reaction

    A Combination Reaction or a Synthesis Reaction is a general category of a chemical reaction , in which two or more reagents are chemical bond together to produce a single product ....
     or synthesis
    Chemical synthesis

    In chemistry, chemical synthesis is purposeful execution of chemical reactions in order to get a product , or several products. This happens by physics and chemical manipulations usually involving one or more reactions....
    , in which 2 or more chemical elements or compounds unite to form a more complex product:
N
Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
2 + 3 H
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
2 ? 2 NH3
Ammonia

Ammonia is a chemical compound with the chemical formula nitrogenhydrogen. It is normally encountered as a gas with a characteristic pungent odor....
  • Chemical decomposition
    Chemical decomposition

    Chemical decomposition or analysis is the separation of a chemical compound into chemical element or smaller compounds. It is sometimes defined as the opposite of a chemical synthesis....
     or analysis, in which a compound is decomposed into smaller compounds or elements:
2 H2O
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 ? 2 H2 + O
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
2
  • Single displacement
    Single displacement reaction

    A single-displacement reaction, also called single-replacement reaction, is when an element or ion moves out of one compound and into another....
     or substitution, characterized by an element being displaced out of a compound by a more reactive
    Reactivity series

    In introductory chemistry, the reactivity series or activity series is an empirical series of metals, in order of "reactivity" from highest to lowest....
     element:
2 Na
Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
(s) + 2 HCl
Hydrogen chloride

The Chemical compound hydrogen chloride has the chemical formula HydrogenChlorine. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity....
(aq) ? 2 NaCl
Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
(aq) + H2(g)
  • Metathesis or Double displacement reaction, in which two compounds exchange ion
    Ion

    An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
    s or bonds to form different compounds:
NaCl(aq) + AgNO3
Silver nitrate

Silver nitrate, also known as lunar caustic, is a soluble chemical compound with chemical formula silverNitrogenOxygen3. This compound is a versatile precursor to many other silver compounds, such as those used in photography....
(aq) ? NaNO3
Sodium nitrate

Sodium nitrate is the chemical compound with the chemical formula NaNO3. This salts, also known as "Chile saltpeter" or "Peru saltpeter" , is a white solid which is very soluble in water....
(aq) + AgCl
Silver chloride

Silver chloride is a chemical compound with the chemical formula SilverChlorine. This white crystalline solid is well known for its low solubility in water ....
(s)
  • Acid-base reactions, broadly characterized as reactions between an acid
    Acid

    An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
     and a base
    Base (chemistry)

    In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
    , 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 number
    Oxidation number

    The oxidation number of a central atom in a complex is the charge that it would have if all the ligands were removed along with the electron pairs that were shared with the central atom....
    s of atoms in involved species occur. Those reactions can often be interpreted as transferences of electrons between different molecular sites or species. An example of a redox reaction is:
2 S2O32-(aq) + I2(aq) ? S4O62-(aq) + 2 I-(aq)
In which I2 is reduced to I- and S2O32- (thiosulfate
Thiosulfate

Thiosulfate is an oxyanion of sulfur produced by the reaction of sulfite ions with elemental sulfur in boiling water. Thiosulfate occurs naturally in hot springs and geysers, and is produced by certain biochemical processes....
 anion) is oxidized to S4O62-.
  • Combustion
    Combustion

    Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering....
    , 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
Fluorine

Fluorine is the chemical element with the symbol F and atomic number 9. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F2 molecule....
 ? CF4 + 2 HF
Hydrogen fluoride

Hydrogen fluoride is a chemical compound with the chemical formula HF. It is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers ....
 + SF6
Sulfur hexafluoride

Sulfur hexafluoride is an inorganic compound with the formula . It is a colorless, odorless, non-toxicity and non-flammable gas . has an octahedral geometry, consisting of six fluorine atoms attached to a central sulfur atom....
  • Disproportionation
    Disproportionation

    Disproportionation or dismutation is used to describe two particular types of chemical reaction:* A chemical reaction of the type: 2A ? A' + A" where A, A' and A" are different chemical species....
     with one reactant forming two distinct products varying in oxidation state.
2 Sn2+ ? Sn + Sn4+


Organic reaction
Organic reaction

Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and organic redox reaction....
s encompass a wide assortment of reactions involving compounds
Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered Inorganic compound....
 which have carbon
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
 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
Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules....
s.

Chemical kinetics


The rate
Reaction rate

The reaction rate or rate of reaction for a reactant or product in a particular chemical reaction is intuitively defined as how fast a reaction takes place....
 of a chemical reaction is a measure of how the concentration
Concentration

In chemistry, concentration is the measure of how much of a given chemical substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent....
 or pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
 of the involved substances changes with time. Analysis of reaction rates is important for several applications, such as in chemical engineering
Chemical engineering

Chemical engineering is the branch of engineering that deals with the application of physical science , with mathematics, to the process of converting raw materials or chemicals into more useful or valuable forms....
 or in chemical equilibrium
Chemical equilibrium

In a chemical process, chemical equilibrium is the state in which the Activity or concentrations of the reactants and products have no net change over time....
 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
    Surface area

    Surface area is how much exposed area an object has. It is expressed in square units. If an object has flat Face , its surface area can be calculated by adding together the areas of its faces....
     available for contact between the reactants, in particular solid ones in heterogeneous systems. Larger surface area leads to higher reaction rates.
  • Pressure
    Pressure

    Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
    , by increasing the pressure, you decrease the volume between molecules. This will increase the frequency of collisions of molecules.
  • Activation energy
    Activation energy

    In chemistry, activation energy is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined as the energy that must be overcome in order for a chemical reaction to occur....
    , 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
    Temperature

    In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater 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
    Activation energy

    In chemistry, activation energy is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined as the energy that must be overcome in order for a chemical reaction to occur....
     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
    Electromagnetic radiation

    Electromagnetic radiation takes the form of wave propagation waves in a vacuum or in matter. EM radiation has an electric field and magnetic field component which oscillate in phase perpendicular to each other and to the direction of energy Wave propagation....
    , most notably ultraviolet
    Ultraviolet

    Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays, in the range 400 nanometer to 10 nm, and energies from 3 Electron volt to 124 eV....
    , is needed to promote the breaking of bonds to start the reaction. This is particularly true for reactions involving radicals
    Radical (chemistry)

    In chemistry, radicals are atoms, molecules or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly chemical reaction, so radicals are likely to take part in chemical reactions....
    .


Reaction rates are related to the concentrations of substances involved in reactions, as quantified by the rate law
Rate equation

The rate law or rate equation for a chemical reaction is an equation which links the reaction rate with concentrations or pressures of reactants and constant parameters ....
 of each reaction. Note that some reactions have rates that are independent of reactant concentrations. These are called zero order reactions.

Reactions and Energy

Chemical energy is part of all chemical reactions. Energy is needed to break chemical bonds in the starting substances. As new bonds form in the final substances, energy is released. By comparing the chemical energy of the original substances with the chemical energy of the final substances, you can decide if energy is released or absorbed in the overall reaction.

Exothermic Reactions

A chemical reaction in which energy is released is called an exothermic reaction
Exothermic reaction

An exothermic reaction is a chemical reaction that releases energy in the form of heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:...
. Exo means "go out" or "exit." Thermic means "heat" or "energy." Exothermic reactions can give off energy in several forms. If heat is released in an exothermic reaction, the nearby matter will become warmer. The nearby matter
Matter

In common usage, matter is anything that has both mass and volume . A more rigorous definition is used in science: matter is what atoms and molecules are made of....
 absorbs the heat released by the reaction. The reaction between gasoline and oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
 in a car's engine
Engine

An engine is a mechanical device that produces some form of output from a given input.An engine whose purpose is to produce kinetic energy output from a fuel is called a Wiktionary:prime mover; alternatively, a motor is a device which produces kinetic energy from a preprocessed "fuel" ....
 is an exothermic reaction

See also

  • List of reactions
  • Organic reaction
    Organic reaction

    Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and organic redox reaction....
  • Inorganic chemical reaction
  • List of important publications in chemistry
  • Stoichiometry
    Stoichiometry

    Stoichiometry is the calculation of quantitative relationships of the reactants and Product in a balanced chemical reaction .Etymology...
  • Stoichiometric coefficient
  • Transition state theory
    Transition state theory

    Transition state theory is the theory of the rates of elementary reactions which assumes a special type of equilibrium between reactants and activated complexes....
  • Gas stoichiometry
  • Thermodynamic databases for pure substances
    Thermodynamic databases for pure substances

    Thermodynamics databases contain information about List of thermodynamic properties for substances, the most important being enthalpy, entropy, and Gibbs free energy....
  • Autocatalytic reaction
    Autocatalytic reaction

    Autocatalytic reactions are chemical reactions in which at least one of the Product is also a reactant. The rate equations for autocatalytic reactions are fundamentally nonlinear....
  • Coefficients
  • Q values
    Q values

    In nuclear physics and nuclear chemistry, the Q value for a nuclear reaction is the amount of energy released by that reaction:A reaction with a positive Q value is exothermic, i.e., has a net release of energy, whilst a reaction with a negative Q value is endothermic, i.e., requires a net energy input....


Further reading

  • Is This Reaction a Substitution, Oxidation-Reduction, or Transfer? / N.S.Imyanitov. J. Chem. Educ. 1993, 70(1), 14 – 16.


External links

  • on chemical reactions