page_title: Chemical reaction
section_title: Oxidation and reduction
hierarchical_section_title: Chemical reaction / Reaction types / Oxidation and reduction
caption_attribution_description: العربية: تمثيل لعملية أكسدة-اختزال. Ελληνικά: Η2 + F2 ⟶ 2HF. English: Illustration of a redox reaction. Euskara: Erredox erreakzio baten irudikapena. Bahasa Indonesia: Ilustrasi sebuah reaksi redoks. Italiano: Illustrazione di una reazione redox. 日本語: 酸化還元反応の例。水素は酸化され、フッ素は還元されている。. Latviešu: Redoksreakcijas piemērs - ūdeņradis atdod savus elektronus sevišķi spēcīgam oksidētājam - fluoram un rodas fluorūdeņradis. Македонски: Илустрација на редокс реакција. Português: Ilustração de uma reação redox. ไทย: ปฏิกิริยารีดอกซ์. اردو: تخسیدی تعامل کی وضاحت. 粵語: 氧化還原反應圖解.
context_page_description: A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei, and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.
  The substance initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which symbolically present the starting materials, end products, and sometimes intermediate products and reaction conditions.
context_section_description: Redox reactions can be understood in terms of transfer of electrons from one involved species (reducing agent) to another (oxidizing agent). In this process, the former species is oxidized and the latter is reduced. Though sufficient for many purposes, these descriptions are not precisely correct. Oxidation is better defined as an increase in oxidation state, and reduction as a decrease in oxidation state. In practice, the transfer of electrons will always change the oxidation state, but there are many reactions that are classed as "redox" even though no electron transfer occurs (such as those involving covalent bonds).
  In the following redox reaction, hazardous sodium metal reacts with toxic chlorine gas to form the ionic compound sodium chloride, or common table salt:
  In the reaction, sodium metal goes from an oxidation state of 0 (as it is a pure element) to +1: in other words, the sodium lost one electron and is said to have been oxidized. On the other hand, the chlorine gas goes from an oxidation of 0 (it is also a pure element) to −1: the chlorine gains one electron and is said to have been reduced. Because the chlorine is the one reduced, it is considered the electron acceptor, or in other words, induces oxidation in the sodium – thus the chlorine gas is considered the oxidizing agent. Conversely, the sodium is oxidized or is the electron donor, and thus induces reduction in the other species and is considered the reducing agent.
  Which of the involved reactants would be reducing or oxidizing agent can be predicted from the electronegativity of their elements. Elements with low electronegativity, such as most metals, easily donate electrons and oxidize – they are reducing agents. On the contrary, many ions with high oxidation numbers, such as H
  ₂O
  ₂, MnO⁻
  ₄, CrO
  ₃, Cr
  ₂O²⁻
  ₇, OsO
  ₄ can gain one or two extra electrons and are strong oxidizing agents.
  The number of electrons donated or accepted in a redox reaction can be predicted from the electron configuration of the reactant element. Elements try to reach the low-energy noble gas configuration, and therefore alkali metals and halogens will donate and accept one electron respectively. Noble gases themselves are chemically inactive.
  An important class of redox reactions are the electrochemical reactions, where electrons from the power supply are used as the reducing agent. These reactions are particularly important for the production of chemical elements, such as chlorine or aluminium. The reverse process in which electrons are released in redox reactions and can be used as electrical energy is possible and used in batteries.
caption: Illustration of a redox reaction
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