Redox

Redox (short for reduction–oxidation reaction) (pronunciation: or ) is a chemical reaction in which the oxidation states of atoms are changed.

The oxidation state, sometimes referred to as oxidation number, describes the degree of oxidation (loss of electrons) of an atom in a chemical compound.

As an example, during the combustion of wood, oxygen from the air is reduced, gaining electrons from carbon which is oxidized.

Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke.

The reaction can occur relatively slowly, as with the formation of rust, or more quickly, in the case of fire.

Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.

Any such reaction involves both a reduction process and a complementary oxidation process, two key concepts involved with electron transfer processes.

ET is a mechanistic description of a redox reaction, wherein the oxidation state of reactant and product changes.

The word oxidation originally implied reaction with oxygen to form an oxide, since dioxygen (O 2 (g)) was historically the first recognized oxidizing agent.

In chemistry, an oxidizing agent (oxidant, oxidizer) is a substance that has the ability to oxidize other substances — in other words to cause them to lose electrons.

There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO 2 ) or the reduction of carbon by hydrogen to yield methane (CH 4 ), and more complex processes such as the oxidation of glucose (C 6 H 12 O 6 ) in the human body.

It is an unwanted byproduct in many large scale oxidation processes, for example, in the production of acrylic acid (over 5 million tons/year).

There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO 2 ) or the reduction of carbon by hydrogen to yield methane (CH 4 ), and more complex processes such as the oxidation of glucose (C 6 H 12 O 6 ) in the human body.

Although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper, which are weaker reducing agents at room temperature.

There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO 2 ) or the reduction of carbon by hydrogen to yield methane (CH 4 ), and more complex processes such as the oxidation of glucose (C 6 H 12 O 6 ) in the human body.

Partial oxidation to methanol, for example, is challenging because the reaction typically progresses all the way to carbon dioxide and water even with an insufficient supply of oxygen.

The oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction. Each half-reaction has a standard electrode potential (E), which is equal to the potential difference or voltage at equilibrium under standard conditions of an electrochemical cell in which the cathode reaction is the half-reaction considered, and the anode is a standard hydrogen electrode where hydrogen is oxidized:

A half reaction is either the oxidation or reduction reaction component of a redox reaction.

And, because it "accepts" electrons, the oxidizing agent is also called an electron acceptor.

It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process.

Substances that have the ability to reduce other substances (cause them to gain electrons) are said to be reductive or reducing and are known as reducing agents, reductants, or reducers.

A reducing agent (also called a reductant or reducer) is an element (such as calcium) or compound that loses (or "donates") an electron to another chemical species in a redox chemical reaction.

Electropositive elemental metals, such as lithium, sodium, magnesium, iron, zinc, and aluminium, are good reducing agents.

Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust.

And, because it "donates" electrons, the reducing agent is also called an electron donor.

It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process.

Electropositive elemental metals, such as lithium, sodium, magnesium, iron, zinc, and aluminium, are good reducing agents.

Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments.

The word reduction originally referred to the loss in weight upon heating a metallic ore such as a metal oxide to extract the metal.

The reductive dissolution of a transition metal oxide occurs when dissolution is coupled to a redox event.

Oxygen is the quintessential oxidizer.

Lavoisier conducted the first adequate quantitative experiments on oxidation and gave the first correct explanation of how combustion works.

The electrochemist John Bockris has used the words electronation and deelectronation to describe reduction and oxidation processes respectively when they occur at electrodes.

The anode is now defined as the electrode at which electrons leave the cell and oxidation occurs (indicated by a minus symbol, "−"), and the cathode as the electrode at which electrons enter the cell and reduction occurs (indicated by a plus symbol, "+").

Redox (short for reduction–oxidation reaction) (pronunciation: or ) is a chemical reaction in which the oxidation states of atoms are changed.

Redox reactions can be understood in terms of transfer of electrons from one involved species (reducing agent) to another (oxidizing agent).

Electropositive elemental metals, such as lithium, sodium, magnesium, iron, zinc, and aluminium, are good reducing agents.

Sulfides formed as the crust solidified under the reducing conditions of the early Earth's atmosphere.

Another method of reduction involves the use of hydrogen gas (H 2 ) with a palladium, platinum, or nickel catalyst.

Nickel is slowly oxidized by air at room temperature and is considered corrosion-resistant.

There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO 2 ) or the reduction of carbon by hydrogen to yield methane (CH 4 ), and more complex processes such as the oxidation of glucose (C 6 H 12 O 6 ) in the human body.

Through glycolysis and later in the reactions of the citric acid cycle and oxidative phosphorylation, glucose is oxidized to eventually form carbon dioxide and water, yielding energy mostly in the form of ATP.

The reduction of nitrate to nitrogen in the presence of an acid (denitrification):

Facultative anaerobic bacteria perform denitrification as a type of respiration that reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter.

Each half-reaction has a standard electrode potential (E), which is equal to the potential difference or voltage at equilibrium under standard conditions of an electrochemical cell in which the cathode reaction is the half-reaction considered, and the anode is a standard hydrogen electrode where hydrogen is oxidized:

An electrolytic cell is an electrochemical cell that drives a non-spontaneous redox reaction through the application of electrical energy.

Each half-reaction has a standard electrode potential (E), which is equal to the potential difference or voltage at equilibrium under standard conditions of an electrochemical cell in which the cathode reaction is the half-reaction considered, and the anode is a standard hydrogen electrode where hydrogen is oxidized:

In a galvanic cell, the anode is the electrode at which the oxidation reaction occurs.

There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO 2 ) or the reduction of carbon by hydrogen to yield methane (CH 4 ), and more complex processes such as the oxidation of glucose (C 6 H 12 O 6 ) in the human body.

is produced in chemistry and biology laboratories, often as a by-product of other reactions; in industry for the hydrogenation of unsaturated substrates; and in nature as a means of expelling reducing equivalents in biochemical reactions.