A chemical reaction is a process that always results in the interconversion of chemical substances A chemical substance is a material with a specific chemical composition.[citation needed] 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. He deduced that, "All samples of a compound have the.^[1] The substance or substances initially involved in a chemical reaction are called reactants A reagent or reactant is a substance or compound consumed during a chemical reaction. Solvents and catalysts, although they are involved in the reaction, are usually not referred to as reactants. Chemical reactions are usually characterized by a chemical change In a chemical change, 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. Some exothermic reactions may be hot enough to cause certain chemicals to also undergo a change in state; for example in the case of aqueous, and they yield one or more products 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 equilibria in complex systems may require years or even centuries to be established. For example, equilibria in groundwater, which usually have properties different from the reactants. Classically, chemical reactions encompass changes that strictly involve the motion of electrons The electron is a subatomic particle that carries a negative electric charge. It has no known substructure and is believed to be a point particle. Electrons participate in gravitational, electromagnetic and weak interactions. Like its rest mass and elementary charge, the intrinsic angular momentum of an electron has a constant value. In the in the forming and breaking of chemical bonds 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. The explanation of the attractive forces is a complex area that is described by the laws of quantum electrodynamics. In practice, however, chemists usually, although the general concept of a chemical reaction, in particular the notion of a 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 numbers. The first chemical equation was diagrammed by Jean Beguin in 1615, is applicable to transformations of elementary particles 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 reactions In nuclear physics, a nuclear reaction is the process in which two nuclei or nuclear particles collide to produce products different from the initial particles. In principle a reaction can involve more than three particles colliding, but because the probability of three or more nuclei to meet at the same time at the same place is much less than. Different chemical reactions are used in combination in chemical synthesis In chemistry, chemical synthesis is purposeful execution of chemical reactions in order to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions. In modern laboratory usage, this tends to imply that the process is reproducible, reliable, and established to work in multiple in order to get a desired product. In biochemistry Biochemistry is the study of the chemical 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 is the process in which the rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. The catalyst may participate in multiple chemical transformations. Catalysts by enzymes Enzymes are biomolecules that catalyze chemical reactions. Nearly all known enzymes are proteins. However, certain RNA molecules can be effective biocatalysts too. These RNA molecules have come to be known as ribozymes. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into form metabolic pathways In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function properly. Because of the many chemicals that may be, 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 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. A-B-C → B-A-C . In some molecules and under some conditions, isomerisation occurs spontaneously. Many isomers are equal or roughly equal in bond energy, and so exist in roughly, in which a chemical compound undergoes a structural rearrangement without any change in its net atomic composition; see stereoisomerism Structural isomers share the same molecular formula, but the bond connections and/or their order between different atoms/groups differs. In stereoisomers, the order and bond connections of the constituent atoms remains the same, but their orientation in space differs
• Direct combination A Combination Reaction or a Synthesis Reaction is a general category of a chemical reaction , in which two or more reagents are chemically bonded together to produce a single product.when two or more substances combine to form a single product, it is known as a combination reaction or synthesis In chemistry, chemical synthesis is purposeful execution of chemical reactions in order to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions. In modern laboratory usage, this tends to imply that the process is reproducible, reliable, and established to work in multiple, in which 2 or more chemical elements or compounds unite to form a more complex product:

N Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere₂ + 3 H Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H2. With an atomic weight of 1.00794 u, hydrogen is the lightest element₂ → 2 NH₃ Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block

• Chemical decomposition Chemical decomposition or analysis is the separation of a chemical compound into elements or smaller compounds. It is sometimes defined as the opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction. The stability that a chemical compound ordinarily has is eventually limited when exposed to extreme or analysis, in which a compound is decomposed into smaller compounds or elements:

2 H₂O Water is a ubiquitous chemical substance that is essential for the survival of all known forms of life.[citation needed] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71% of the Earth's surface. On Earth, it is found mostly in → 2 H₂ + O Oxygen (pronounced /ˈɒksɨdʒɨn/, from the Greek roots ὀξύς (acid, literally "sharp," from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O. It is a member of the chalcogen group on the periodic table, and is a highly reactive₂

• Single displacement A single-displacement reaction, also called single-replacement reaction, is a type of oxidation-reduction chemical reaction when an element or ion moves out of one compound and into another. This is usually written as or substitution In a substitution reaction, a functional group in a particular chemical compound is replaced by another group . In organic chemistry, the electrophilic and nucleophilic substitution reactions are of prime importance. Organic substitution reactions are classified in several main organic reaction types depending on whether the reagent that brings, characterized by an element being displaced out of a compound by a more reactive In introductory chemistry, the reactivity series or activity series is an empirical series of metals, in order of "reactivity" from highest to lowest. It is used to summarize information about the reactions of metals with acids and water, single displacement reactions and the extraction of metals from their ores element:

2 Na Sodium is a metallic element with a symbol Na (from Latin natrium or Arabic natrun) and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1" (formerly known as ‘group IA’). It has only one stable isotope, 23Na(s) + 2 HCl The compound hydrogen chloride has the formula H (aq) An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending to the relevant formula. The word aqueous means pertaining to, related to, similar to, or dissolved in water. As water is an excellent solvent as well as naturally abundant, it is a ubiquitous solvent in chemistry → 2 NaCl Sodium chloride, also known as common salt, table salt, or halite, is an ionic compound with the formula Na (aq) + H₂(g)

• Metathesis These chemical species can either be ionic or covalent. When referring to precipitation reactions between solutions of ions in inorganic chemistry, these were formerly referred to as double displacement or double replacement reactions, though these terms are still encouraged.[citation needed] or Double displacement reaction, in which two compounds exchange ions An ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge or bonds to form different compounds:

NaCl(aq) + AgNO₃ Silver nitrate, also known as lunar caustic, is a soluble chemical compound with chemical formula Ag (aq) → NaNO₃ Sodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as "Chile saltpeter" or "Peru saltpeter" , is a white solid which is very soluble in water. The mineral form is also known as nitratine or soda niter(aq) + AgCl Silver chloride is a chemical compound with the chemical formula Ag (s)

• Acid-base An acid-base reaction is a chemical reaction that occurs between an acid and a base. Several concepts that provide alternative definitions for the reaction mechanisms involved and their application in solving related problems exist. Despite several differences in definitions, their importance becomes apparent as different methods of analysis when reactions, broadly characterized as reactions between an 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. a pH less than 7.0. That approximates the modern definition of Johannes Nicolaus Brønsted and Martin Lowry, who independently defined an acid as a compound which donates a hydrogen and a base In chemistry, a base is most commonly thought of as an aqueous substance that can accept hydrogen ions. A base is also often referred to as an alkali if OH− ions are involved. This refers to the Brønsted-Lowry theory of acids and bases. Alternate definitions of bases include electron pair donors , as sources of hydroxide anions (Arrhenius). In, can have different definitions depending on the acid-base concept employed. Some of the most common are:
  • Arrhenius An acid-base reaction is a chemical reaction that occurs between an acid and a base. Several concepts that provide alternative definitions for the reaction mechanisms involved and their application in solving related problems exist. Despite several differences in definitions, their importance becomes apparent as different methods of analysis when definition: Acids dissociate in water releasing H₃O⁺ ions; bases dissociate in water releasing OH^- ions.
  • Brønsted-Lowry In chemistry, the Brønsted-Lowry theory is an acid-base theory, proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923. In this system, an acid is defined as any chemical species that is able to lose, or "donate" a hydrogen ion (proton), and a base is a species with the ability to gain or "accept" definition: Acids are proton (H⁺) donors; bases are proton acceptors. Includes the Arrhenius definition.
  • Lewis An acid-base reaction is a chemical reaction that occurs between an acid and a base. Several concepts that provide alternative definitions for the reaction mechanisms involved and their application in solving related problems exist. Despite several differences in definitions, their importance becomes apparent as different methods of analysis when definition: Acids are electron-pair acceptors; bases are electron-pair donors. Includes the Brønsted-Lowry definition.
• Redox reactions Redox 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, in which changes in oxidation numbers The oxidation number of a central atom in a coordination compound 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. It is used in the nomenclature of inorganic compounds. It is represented by a Roman numeral; the plus sign is omitted for positive oxidation numbers 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 S₂O₃^2- (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. It instantly dechlorinates water, and is notable for its use to halt bleaching in the paper-making industry. Thiosulfate is anion) is oxidized to S₄O₆^2-.

• 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 is a chemical element, represented by the symbol F, and the atomic number 9. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F2 molecule. F2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the most chemically reactive and electronegative of all the elements. For → CF₄ Tetrafluoromethane, also known as carbon tetrafluoride, is the simplest fluorocarbon . It has a very high bond strength due to the nature of the carbon–fluorine bond. It can also be classified as a haloalkane or halomethane. Because of the multiple carbon–fluorine bonds, and the highest electronegativity of fluorine, the carbon in + 2 HF Hydrogen fluoride is a chemical compound with the 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 . HF is widely used in the petrochemical industry and a component of many superacids. HF boils + SF₆ Sulfur hexafluoride is an inorganic, colorless, odorless, non-toxic and non-flammable gas (under standard conditions). SF6 has an octahedral geometry, consisting of six fluorine atoms attached to a central sulfur atom. It is a hypervalent molecule. Typical for a nonpolar gas, it is poorly soluble in water but soluble in nonpolar organic solvents

• Disproportionation with one reactant forming two distinct products varying in oxidation state.

2 Sn²⁺ → Sn + Sn⁴⁺

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.

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 ultraviolet, 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.

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. 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 absorbs the heat released by the reaction. The reaction between gasoline and oxygen in a car's engine is an exothermic reaction

See also

• List of reactions
• Organic reaction
• Inorganic chemical reaction
• List of important publications in chemistry
• Stoichiometry
• Stoichiometric coefficient
• Transition state theory
• Gas stoichiometry
• Thermodynamic databases for pure substances
• Autocatalytic reaction
• Coefficients
• Q values

Further reading

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

References

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

External links

• UC Berkeley video lecture on chemical reactions

Categories: Chemical reactions | Chemistry

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• Chemical Reaction
• Chemical Biology
• Chemical Process
• Chemical Compound
• Chemical Engineer

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