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Материалы IV студенческой конференции «химия. Экология. Медицина» направления работы - страница №15/19

NAMED REACTIONS IN CHEMISTRY

Ekong Anita Willie, group 3. Scientific adviser is Svetlana Kozub.


chemical reaction is a process that leads to the transformation of one set of chemical substances to another.[1] Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bondsbetween atoms, and can often be described by a chemical equation.

The substance (or substances) 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 graphically present the starting materials, end products, and sometimes intermediate products and reaction conditions.

Chemical reactions happen at a characteristic reaction rate at a given temperature and chemical concentration, and rapid reactions are often described as spontaneous, requiring no input of extra energy other than thermal energy. Non-spontaneous reactions run so slowly that they are considered to require the input of some type of additional energy (such as extra heat, light or electricity) in order to proceed to completion (chemical equilibrium) at human time scales.

Different chemical reactions are used in combinations during in chemical synthesis in order to obtain a desired product. In biochemistry, a similar series of chemical reactions form metabolic pathways. These reactions are often catalyzed by protein enzymes. These enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions may be performed at the temperatures and concentrations present within a cell.

The general concept of a chemical reaction has been extended to non-chemical reactions between entities smaller than atoms, includingnuclear reactionsradioactive decays, and reactions between elementary particles as described by quantum field theory.

CYANIDE AS AN ELEMENT

Gyasi Confidense, group 5. Scientific adviser is Svetlana Kozub.


Cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the polyatomic anion CN, which is isoelectronic with carbon monoxide and with molecular nitrogen. Most cyanides are highly toxic.

Sources Of Cyanide

Nearly 1,500 plants are known to contain cyanide, generally in the form of sugars or lipids. Cyanic glucoside can be found in varying amounts in Johnson Grass, peach seeds, cherry pits, apple seeds, green beans, bitter almonds, peas, apricots, cassava root, elderberries, flax seeds, choke cherries and bamboo shoots. The bamboo shoot contains the highest amount of cyanic glucoside or cyanide sugar.



The Chemical and Physical Properties of Hydrogen Cyanide

* The chemical formula of cyanide is CN-, and the hydrogen cyanide is HCN.


* Molecular weight: 27.03
* Boiling point (at 760 mm Hg): 26 degrees C (79 degrees F)
* Specific gravity: 0.7 at 20 degrees C (68 degrees F)
* Vapor density: 0.94
* Melting point: -13.4 degrees C (7.88 degrees F)
* Vapor pressure at 20 degrees C (68 degrees F): 620 mm Hg
* Solubility: Miscible with water and alcohol, and slightly soluble in ether.
* Hydrogen cyanide is a colorless, extremely poisonous, and highly volatile liquid that boils slightly above room temperature at 26 °C (78.8 °F).
* HCN has a faint, bitter, almond-like odor that some people are unable to detect due to a genetic trait.

Clemmensen reduction

Ahmed Ali Al-majrabi, group 5. Scientific adviser is Svetlana Kozub.


Clemmensen reduction is a chemical reaction described as a reduction of ketones (or aldehydes) to alkanes using zinc amalgam and hydrochloric acid.[1][2][3] This reaction is named after Erik Christian Clemmensen, a Danish chemist.[4]
The Clemmensen reduction is particularly effective at reducing aryl-alkyl ketones.[5][6] With aliphatic or cyclic ketones, zinc metal reduction is much more effective.[7]

The substrate must be stable in the strongly acidic conditions of the Clemmensen reduction. Acid sensitive substrates should be reacted in the Wolff-Kishner reduction, which utilizes strongly basic conditions; a further, milder method is the Mozingo reduction. As a result of Clemmensen Reduction, the carbon of the carbonyl group involved is converted from sp2 hybridisation to sp3 hybridisation. The oxygen atom is lost in the form of one molecule of water.

References:

Clemmensen, E. (1913). Chemische Berichte 46: 1837.

Clemmensen, E. (1914). Chemische Berichte 47: 51.

Clemmensen, E. (1914). Chemische Berichte 47: 681.

Biographies of Chemists, accessed 6 Feb 2007

Reviews:


Martin, E. L. (1942). Org. React. 1: 155.

Buchanan, J. G. St. C.; Woodgate, P. D. (1969). "The Clemmensen reduction of difunctional ketones". Quart. Rev. 23: 522. doi:10.1039/QR9692300522.

Vedejs, E. (1975). Org. React. 22: 40.

Yamamura, S.; Nishiyama, S. (1991). Comp. Org. Syn. 8: 309–313.



NAMED CHEMICAL REACTIONS

Imo Udoidiok, group 5. Scientific adviser is Svetlana Kozub.


All chemical reactions can be placed into one of six categories.  Here they are, in no particular order:

1) Combustion: A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat. An example of this kind of reaction is the burning of napthalene:



C10H8 + 12 O2 ---> 10 CO2 + 4 H2O

2) Synthesis: A synthesis reaction is when two or more simple compounds combine to form a more complicated one. These reactions come in the general form of:



A + B ---> AB

One example of a synthesis reaction is the combination of iron and sulfur to form iron (II) sulfide:



8 Fe + S8 ---> 8 FeS

3) Decomposition: A decomposition reaction is the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. These reactions come in the general form:



AB ---> A + B

One example of a decomposition reaction is the electrolysis of water to make oxygen and hydrogen gas:



2 H2O ---> 2 H2 + O2

4) Single displacement: This is when one element trades places with another element in a compound. These reactions come in the general form of:



A + BC ---> AC + B

One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:



Mg + 2 H2O ---> Mg(OH)2 + H2

5) Double displacement: This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form:



AB + CD ---> AD + CB

One example of a double displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:



Pb(NO3)2 + 2 KI ---> PbI2 + 2 KNO3

6) Acid-base: This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H+ ion in the acid reacts with the OH- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water:



HA + BOH ---> H2O + BA

One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide:



HBr + NaOH ---> NaBr + H2O

[references: http://misterguch.brinkster.net/6typesofchemicalrxn.html]

METALS ARE EARTH’S TREASURES

Shahubaan Rasheed Ahmed, group 6. Scientific adviser is Larisa Lykyanova.


Metals are an integral part of our planet and are found in almost all rocks and soils. Most metals form compounds, called minerals, which are naturally occurring, inorganic solids with regular chemical compositions and crystal structures. Although most metal-bearing mineral compositions comprise several elements, there are a few exceptions such as gold, which is found in its elemental form as a mineral called native gold.

Metals can form, or be part of, many different minerals. The number of metals (over 70 in the periodic table) and their compounds results in an enormous array of minerals. Iron, for instance, which is very abundant in nature, is found in over 1100 minerals*. The brilliant colors frequently associated with gems such as emerald, ruby and sapphire reflect the variety of metal-containing minerals. Chalcopyrite, an important copper-bearing mineral, is bright yellow, while the copper-phosphate mineral, turquoise, has a blue color.

Minerals combine to become the rocks that make up our planet. Most rocks form considerably below the surface of the earth under the influence of pressure and heat. Geologic processes can cause them to move upward toward the surface. There, in the presence of oxygen and water, they break down, releasing elements - including metals - into solutions, and forming new minerals. This process, known as weathering, forms our soils. From soil, metals are taken up by plants and then by animals and humans in food. As soils are eroded, metal-bearing sediment is carried into streams and rivers, and eventually into the ocean. These sediments contribute to new rocks through ongoing geologic processes.

Metals are ubiquitous in nature, and their distribution in the earth depends on geologic processes that have taken place. Some processes may form minerals with high metal contents; rocks containing these minerals may be so enriched that they can be mined at a profit - becoming ore deposits. Rocks that contain lower enrichments are known simply as mineral deposits. The metal content of deposits can range from a few parts per million (ppm) to as much as 650,000 ppm (65%) in the case of some iron ores. Mining companies employ special technologies to extract metals from complex ores in the production of pure metals such as iron, aluminum, copper and gold.

While high concentrations of metals may lead to the formation of deposits, in many cases where the concentration of a metal is low, the metal may simply replace, or substitute for, another element in the crystal structure of common minerals. For example, rocks that make up the sea floor contain high concentrations of the metal magnesium, as well as smaller concentrations of nickel which substitute for some of the magnesium. Similarly, rocks that make up the continents can contain lead, which substitutes for the more abundant metallic element, potassium. This substitution phenomenon leads to the wide distribution of many metals at low concentrations throughout the rocks of the earth.



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