Redox

A redox reaction (pronounced redóksreaktion, actually: oxidation-reduction reaction ) is a chemical reaction in which a reactant electron transfers to the other. This case, therefore (reduction) find an electron discharge (oxidation) rather than by a substance and an electron micrograph. Redox reactions are of fundamental importance in chemistry: Many metabolic and combustion processes, technical production processes and detection reactions based on such electron transfer reactions.

• 3.6.1 Cellular Respiration and Photosynthesis
• 3.6.2 alcoholic fermentation
• 3.6.3 methane formation

• 3.7.1 Galvanic Cells, batteries and electrolysis

Reaction sequence

At each redox reaction, a substance A, which emits electrons responsive (reducing agent, known donor ) with at least one substance B which receives the electrons (oxidation means acceptor). The general reaction schemes are as follows:

To determine which substance is oxidized or reduced in a reaction, the formal oxidation number can be used.

Special cases

At a comproportionation (or: synproportionation ) reacting compounds containing an element in a low oxidation state (reducing agent), together with compounds in which the element in a higher oxidation state (oxidizing agent ) is present, to form a compound with an average oxidation state.

One speaks of a disproportionation, on condition that during a chemical reaction elements with medium oxidation state in those with a low and a higher one. These reactions often take place under the influence of a catalyst ( material which accelerate a chemical reaction, without changing it) from.

Examples

The reaction of hydrogen with oxygen ( oxyhydrogen ), in water (H2O ) is produced, hydrogen-oxygen reaction is called. Each combustion is an oxidation-reduction reaction dar. Thus also the burning of gasoline, diesel fuel and kerosene in motor vehicles, ships and aircraft. Fuels, which release a lot of energy can be used as rocket fuel. In pyrotechnics is also set to oxidizing and reducing agents for various fireworks effects. For explosives it comes to a sudden exothermic redox reaction in the gas is free to expand strongly temperature-dependent and thus causes the explosive force.

Metal oxide formation

Reacts a metal atom having an oxygen atom, it is possible to understand the oxidation of the metal according to the following reaction equations:

Oxygen in this case the desire to build by taking up two electrons stable Valenzelektronenschale with a total of eight electrons ( octet rule ). The metal in turn can dissolve by delivering the electrons partially occupied shells and reach the next lower stable electron configuration. When iron is oxidized, the result is known from the everyday rust. When active cathodic corrosion protection again oxidation-reduction reactions are exploited.

Large-scale redox

The combustion of fossil fuels such as coal, petroleum, natural gas is used in thermal power plants to generate electrical energy. Numerous reactions from the field of metallurgy are classic examples of industrially important redox reactions in the industry.

Blast furnace process

In the blast furnace process, iron is reduced with coke. As a side reaction occurs, among other things, the strong reducing agent carbon monoxide, which is not further react with oxygen deficiency in the blast furnace immediately to carbon dioxide.

Thermite

For the preparation of various metals from their oxides can be used as a reducing agent aluminum, when the metals more noble than aluminum. The method used in the aluminum powder or chips, ie aluminothermic process. A mixture of iron oxide and aluminum thermite is called and is used for example for welding railroad rails and fire bombs.

Food

In the manufacture of margarine Vegetable oils are the catalytically hydrogenated ( Hydrogenation ).

The reddening of meat by curing salts is also a redox reaction. It leads to the formation of stable complexes bright red in color ( nitrosylmyoglobin and Nitrosylmetmyoglobin ).

Fatty foods are added to oxidation damage to the product (and thus rancidity ) to prevent antioxidants. Instead, the added antioxidants are attacked by oxidation.

Analysis

Numerous analytical methods are based on redox processes. Classical detection reactions or separation programs are partly based on redox reactions. Likewise, modern electrochemical methods of analysis and the quantitative redox titration.

Synthetic chemistry

In the Haber- Bosch process of ammonia from the elements nitrogen and hydrogen is produced. This is among other things an important precursor material for the manufacture of nitrogen fertilizer for agriculture and thus of enormous significance of an oxidizing or reducing agent measurable.

Biochemistry

Many cellular processes involve redox reactions. Frequently involved are the coenzymes NAD, NADP and FAD, transfer the reducing agent in the form of hydride ions. These reducing equivalents are often used to convert energy by substrate chain or oxidative phosphorylation in the form of GTP or ATP.

Cellular respiration and photosynthesis

In cellular respiration glucose (dextrose ) is oxidized to carbon dioxide and reduces oxygen to water. The simplified chemical formula:

The reverse reaction is photosynthesis from carbon dioxide and water in the green plants - by supplying energy ( light) - build dextrose (glucose ) and release oxygen. The overall reaction equation is:

Alcoholic fermentation

Organisms such as baker's yeast can convert to drinking alcohol and carbon dioxide to derive energy during alcoholic fermentation of sugar.

Methane formation

Archaebacteria from the group of methanogens can be produced from carbon dioxide anaerobically methane. The process is called methanogenesis.

Electrochemistry

Electrochemistry is the branch of physical chemistry, which deals with the relationship between electrical and chemical processes. Therefore, when an oxidation-reduction reaction by an electrical current is forced or delivered such, this is an electrochemical process. The key for electrochemistry processes during these processes at the phase boundary. Electrochemistry is the science of the processes between an electron conductor ( electrode) and an ionic conductor (electrolyte). Of central importance is the Nernst equation describing the concentration dependence of the electrode potential. This can be achieved using the redox titration to determine analytically utilize ion in solution. Theoretically, the transfer of outer electrons in solution by the Marcus theory is described.

Galvanic Cells, batteries and electrolysis

The redox reaction is enforced by an externally applied electrical current, this operation is called electrolysis - is caused by the chemical reaction of appropriate substances, a measurable voltage is present as a galvanic element. These voltages ( redox potential ) are recorded characteristic of the respective reactions, and on a scale that the electrochemical series. Here the strength of an oxidizing or reducing agent is measurable.

The electrochemical redox reactions run in a galvanic cell from:

• During the electrolysis, and the charging of a battery case, electrical energy is supplied.
• When discharging a battery or power extraction from a fuel cell to obtain electrical energy, which corresponds to the reversible case with a near zero electric current ( I = 0) the Gibbs energy of the reaction.