- Also called:
- redox reaction
oxidation-reduction reaction
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What is an oxidation-reduction (redox) reaction?
An oxidation-reduction (redox) reaction is any chemical reaction where the oxidation number of a participating chemical species changes. Redox processes involve a transfer of oxygen atoms, hydrogen atoms, or electrons.
In any oxidation reaction a reciprocal reduction occurs. The reactant that causes the oxidation is the oxidizing agent, and that reagent is reduced by the reducing agent.
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What happens to atoms during a redox reaction?
In a redox reaction, atoms undergo changes in their oxidation states through the gain, loss, or sharing of electrons. Oxidation involves an increase in an atom's oxidation number, signifying a loss of electrons. Conversely, reduction entails a decrease in oxidation number, indicating a gain of electrons. These processes are complementary; as one substance is oxidized, another is reduced. The substance causing oxidation is the oxidizing agent, while the one causing reduction is the reducing agent.
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What does it mean when a substance is oxidized or reduced?
In an oxidation-reduction reaction, also known as a redox reaction, oxidation is the loss of electrons, or the increase in oxidation number, by an atom or group of atoms. Reduction is the gain of electrons, or the decrease in oxidation number, by an atom. Oxidation and reduction reactions are coupled, meaning one cannot occur without the other, and they involve a net chemical change.
The substance that causes oxidation is called the oxidizing agent, while the substance that causes reduction is called the reducing agent.
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How are electrons involved in oxidation and reduction?
In oxidation-reduction (redox) reactions, electrons are transferred between substances. Oxidation involves the loss of electrons, resulting in an increase in the oxidation state of an atom. Conversely, reduction involves the gain of electrons, leading to a decrease in the oxidation state of an atom.
These reactions always occur together: one substance loses electrons (undergoes oxidation) while another gains electrons (undergoes reduction). The substance that causes oxidation by accepting electrons is called the oxidizing agent, while the substance that causes reduction by donating electrons is called the reducing agent. This electron transfer is the basis for energy in batteries, where electrons move from a reducing agent to an oxidizing agent through an external circuit.
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Can you give an example of a redox reaction in everyday life?
A common example of a redox reaction in everyday life is the rusting of iron. Iron reacts with oxygen and water in the air, resulting in the formation of iron dihydroxide, or rust:
[2Fe(s) + 2H_2O(l) + O_2(g) \longrightarrow 2Fe(OH)_2(s)]
In this reaction, iron metal is oxidized to iron dihydroxide, and elemental oxygen acts as the oxidizing agent. Redox reactions are characterized by the transfer of electrons between chemical species, resulting in changes in their oxidation states.
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Why are redox reactions important in biological and industrial processes?
Oxidation-reduction (redox) reactions are essential in both biological and industrial processes because they involve the transfer of electrons between chemical species, leading to changes in their oxidation states.
Biological significance
Redox reactions are the central energy-producing process of life. For example, respiration uses redox reactions to oxidize food, providing energy for cells. Photosynthesis uses redox reactions to convert solar energy into chemical energy by reducing carbon compounds.
Industrial applications
Many industrial processes rely on redox reactions to produce essential chemical products such as ammonia, hydrogen, and metals. Redox reactions are also the source of energy in batteries, where electrons are transferred from a reducing agent to an oxidizing agent through an external circuit.
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oxidation-reduction reaction, any chemical reaction in which the oxidation number of a participating chemical species changes. The term covers a large and diverse body of processes. Many oxidation-reduction reactions are as common and familiar as fire, the rusting and dissolution of metals, the browning of fruit, and respiration and photosynthesisābasic life functions.
Major classifications
Most oxidation-reduction (redox) processes involve the transfer of oxygen atoms, hydrogen atoms, or electrons, with all three processes sharing two important characteristics: (1) they are coupledāi.e., in any oxidation reaction a reciprocal reduction occurs, and (2) they involve a characteristic net chemical changeāi.e., an atom or electron goes from one unit of matter to another. Both reciprocity and net change are illustrated below in examples of the three most common types of oxidation-reduction reactions.
Oxygen-atom transfer
Carbon reacts with mercury(II) oxide (a compound in which mercury has a bonding capacity expressed as +2; see below Oxidation-state change) to produce carbon dioxide and mercury metal. This reaction can be written in equation form:
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Carbon, receiving oxygen, is oxidized; mercury(II) oxide, losing oxygen, undergoes the complementary reduction; and the net change is the transfer of two oxygen atoms from mercury(II) oxide units to a carbon atom.
Hydrogen-atom transfer
Hydrogen atoms are transferred from hydrazine, a compound of nitrogen and hydrogen, to oxygen in the following reaction:
Hydrazine, losing hydrogen, is oxidized to molecular nitrogen, while oxygen, gaining hydrogen, is reduced to water.
Electron transfer
Zinc metal and copper(II) ion react in water solution, producing copper metal and an aqueous (denoted by aq) zinc ion according to the equation
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With the transfer of two of its electrons, the zinc metal is oxidized, becoming an aqueous zinc ion, while the copper(II) ion, gaining electrons, is reduced to copper metal. Net change is the transfer of two electrons, lost by zinc and acquired by copper.
Because of their complementary nature, the oxidation and reduction processes together are referred to as redox reactions. The reactant that brings about the oxidation is called the oxidizing agent, and that reagent is itself reduced by the reducing agent. In the examples given above, mercury(II) oxide, oxygen, and the copper(II) ion are oxidizing agents, and carbon, hydrazine, and zinc are the reducing agents.