Chemical Reaction - The Brønsted-Lowry Theory | Britannica

Substitution, elimination, and addition reactions

chloromethane production
chloromethane productionThe reaction of methane (CH4) and chlorine (Cl2) to form chloromethane (CH3Cl) and hydrochloric acid (HCl).(more)

These terms are particularly useful in describing organic reactions. In a substitution reaction, an atom or group of atoms in a molecule is replaced by another atom or group of atoms. For example, methane (CH4) reacts with chlorine (Cl2) to produce chloromethane (CH3Cl), a compound used as a topical anesthetic. In this reaction, a chlorine atom is substituted for a hydrogen atom.

tetrafluoroethylene production
tetrafluoroethylene productionElimination reaction in which two molecules of chlorodifluoromethane (CHClF2) produce tetrafluoroethylene (C2F4) and two molecules of hydrochloric acid (HCl).(more)

Substitution reactions are widely used in industrial chemistry. For example, substituting two of the chlorine atoms on chloroform (CHCl3) with fluorine atoms produces chlorodifluoromethane (CHClF2). This product undergoes a further reaction when heated strongly. 2CHClF2(g) → F2C=CF2(g) + 2HCl(g) This latter reaction is an example of an elimination reaction, a hydrogen atom and a chlorine atom being eliminated from the starting material as hydrochloric acid (HCl). The other product is tetrafluoroethylene, a precursor to the polymer known commercially as Teflon.

ethanol production
ethanol productionAddition reaction of ethylene (C2H4) with water (H2O) to produce ethanol (C2H5OH).(more)

Addition reactions are the opposite of elimination reactions. As the name implies, one molecule is added to another. An example is the common industrial preparation of ethanol (CH3CH2OH). Historically, this compound was made by fermentation. However, since the early 1970s, it has also been made commercially by the addition of water to ethylene. C2H4+ H2O → CH3CH2OH

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