A chemical reaction is a system that always results in the conversion of reactants into product or products. The substance or substances initially involved in a chemical reaction are called reactants. A type of a chemical reaction is normally characterized by the type of chemical change, and it yields one or exceeding products which are, in general, colorful from the reactants.

Generally speaking, chemical reactions involve changes that strictly cover the motility of electrons in the forming and breaking of chemical bonds. Chemical equations are generally used to define the chemical transformations of elementary particles that befall during the reaction.

Chemical changes are a conclusion of chemical reactions. All chemical reactions comprehend a silver in substances and a alternate in energy. However, neither concern nor power is created or destroyed in a chemical reaction. There are so countless chemical reactions that it is conducive to classify them into differential types including the widely used terms for describing usual reactions.

Combination reaction or synthesis reaction: it is a reaction in which 2 or another chemical elements or compounds unite to appearance a expanded labyrinthine product.

Example: N2 + 3 H2 ' 2 NH3

Isomerisation reaction: is a reaction in which a chemical compound undergoes a structural rearrangement without any copper in its snare atomic composition.

Example: trans-2-butene and cis-2-butene are isomers.

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

Example: 2 Aqua ' 2 H2 + O2

Single displacement or substitution: this type of reaction is characterized by an component activity displaced outside of a compound by a enhanced reactive element.

Example: 2 Na(s) + 2 HCl(aq) ' 2 NaCl(aq) + H2(g)

Metathesis or Coupled displacement reaction: represents a reaction in which two compounds alternate ions or bonds to anatomy at variance compounds

Examples: NaCl(aq) + AgNO3(aq) ' NaNO3(aq) + AgCl(s)

Acid-base reactions: broadly these reactions are characterized as reactions between an acid and a base, can corner disparate definitions depending on the acid-base sense employed. Some of the most colloquial are:

Arrhenius definition: Acids dissociate in irrigate releasing H3O+ ions; bases dissociate in drench releasing OH- ions.

Brшnsted-Lowry definition: Acids are proton (H+) donors; bases are proton acceptors.

Lewis definition: Acids are electron-pair acceptors; bases are electron-pair donors.
Example: HCl(aq) + NaOH(aq) ' NaCl(aq) + H2O(l)

Redox reactions: are reactions in which changes in oxidation numbers of atoms in involved species occur. Those reactions can frequently be interpreted as transfer of electrons between at odds molecular sites or species.

Example: 2 S2O32(aq) + I2(aq) ' S4O62(aq) + 2 I(aq)
In this case, I2 is reduced to I- and S2O32- (thiosulfate anion) is oxidized to S4O62-.

Combustion reaction: it is a congenial of redox reaction in which any combustible substance combines with an oxidizing element, usually oxygen, to create heat and embodiment oxidized products.

Example: C3H8 + 5 Oxygen ' 3 CO2 + 4 H2O

Other types of chemical reactions incorporate biological reactions which are father in organic chemistry.
Organic reactions commit to paper a broad array of reactions involving compounds which bear carbon as the leading element in their molecular structure. In opposition to inorganic reactions, organic chemistry reactions are classified in big division by the types of the functional groups that exist within everyone compound. In this occasion the reactions are described by showing the mechanisms which the changes catch place.

Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are listed bellow:

- Appendix reactions
- Elimination reactions
- Substitution reactions
- Redox reactions
- Rearrangement reactions

- Pericyclic reactions

The typical construction of the SN2 mechanism for case history is as follows:

Where nuc: = nucleophile
X = leaving aggregation (usually halide or tosylate, mesylate)

Example of hydroxide ion that acts as the nucleophile and bromine is the leaving group

This results in the inversion of the configuration now of the bottom charge of the nucleophile.

The solvent type, the electrophile and the leaving group, all play an relevant role in this type of reaction:

Solvents: protic solvents such as h2o and alcohols stabilize the nucleophile so yet that it testament not act with substrate. Therefore, the applicability of a deluxe polar aprotic solvent such as ethers and ketones and halogenated hydrocarbons is required.

Nucleophiles: A bully nucleophile is required thanks to it is involved in the percentage determining step. A flimsy nucleophile will not efficiently encounter the substrate.

Leaving groups: A worthy leaving assemblage is required, such as a halide or a tosylate, because it is involved in the proportion determining process (better leaving troop for halogens: I>Br>Cl>F)
In organic synthesis, organic reactions are used in the interpretation of recent organic molecules. The industry of lousy with man-made chemicals such as drugs, plastics, bite additives, fabrics depend on organic reactions.

Among these, the oldest organic reactions are combustion of organic fuels and saponification of fats to beget soap. Fashionable and advance organic chemistry starts with synthesis of terpenes, carbohydrates, proteins, steroids and polymerization reactions in the eighteen century. In the account of the Nobel Passion in Chemistry, awards gain been inured for the invention of particular organic reactions such as the Grignard reaction in 1912, the Diels-Alder reaction in 1950, the Wittig reaction in 1979 and olefin metathesis in 2005.