CHEMISTRY GLOSSARY

Goldschmidt process    →   Goldschmidtov postupak

Goldschmidt process (thermite process) is a method of extracting metals by reducing the oxide with aluminium powder. Practically all the metallic oxides are reducible by this method, the chief exception being the oxide of magnesium. The thermite process was developed by the German chemist Hans Goldschmidt (1861-1923) in 1893.

Goldschmidt was originally interested in producing very pure metals, but he soon realized the value in welding, a process known as Thermit welding.

Haber process    →   Haberov proces

Haber process is an industrial process for producing ammonia by reaction of nitrogen with hydrogen:

The reaction is reversible and exothermic, so that a high yield of ammonia is favoured by low temperature. However, the rate of reaction would be too slow for equilibrium to be reached at normal temperatures, so an optimum temperature of about 450 °C is used, with a catalyst of iron containing potassium aluminium oxide promoters. The higher the pressure the greater the yield, although there are technical difficulties in using very high pressures. A pressure of about 250 atmospheres is commonly employed. The removal of ammonia from the batch as soon as it is formed ensures that an equilibrium favouring product formation is maintained. The nitrogen is obtained from air. Formerly, the hydrogen was from water gas and the water-gas shift reaction (the Bosch process) but now the raw material (called synthesis gas) is obtained by steam reforming natural gas.

The process is of immense importance for the fixation of nitrogen for fertilisers and explosives. It was developed in 1908 by German chemist Fritz Haber (1868-1934) and was developed for industrial use by Carl Bosch (1874-1940), hence the alternative name Haber-Bosch process.

Ostwald’s process    →   Ostwaldov proces

Ostwald’s process is a process by which the nitric acid can be obtained in three degrees. In the first stage ammonia and oxygen react (with platinum-rhodium as a catalyst), whereby the nitrogen monoxide and water emerge

In the second stage nitrogen monoxide reacts with oxygen whereby nitrogen dioxide emerges

and in the third stage nitrogen dioxide dissolves in water, in the presence of air, giving the nitric acid

reversible process    →   reverzibilan proces

Reversible process or reaction is those that can be reversed by an infinitesimally small change in conditions. For example, ice and water coexist at 101 325 Pa and 0 °C; a very slight temperature increase causes the ice to melt; a tiny temperature decrease causes the water to freeze. Melting or freezing under these conditions can be considered reversible.

spontaneous process    →   spontani proces

Spontaneous process is a process that occurs without outside intervention. No external forces are required to keep the process going, although external forces may be required to get the process started. For example, the burning of wood is spontaneous once the fire is started. The combination of water and carbon dioxide to reform the wood and oxygen is NOT spontaneous! Spontaneity is independent of rate. To be spontaneous a process must increase the entropy of the universe.

Solvay’s process    →   Solvayev postupak

Solvay ’s process is an industrial process for producing sodium carbonate from sodium chloride and ammonia and carbon dioxide.

Carbon dioixide is produced by the thermal decomposition of limestone, CaCO₃(s).

Quicklime, formed as a by-product of the thermal decomposition of limestone, is treated with water to form calcium hydroxide.

Calcium hydroxide is heated with ammonium chloride to form ammonia and calcium chloride (by product).

Carbon dioxide reacts with ammonia to form ammonium carbonate.

Ammonium carbonate further reacts with carbon dioxide to form ammonium bicarbonate.

Ammonium bicarbonate then react with sodium chloride to form sodium bicarbonate.

Dry sodium bicarbonate is heated in rotary furnace to give anhydrous sodium carbonate or soda ash.

The carbon dioxide produced is recycled back into the process.

Ziegler process    →   Zieglerov proces

Ziegler process is an industrial process for the manufacture of high-density polyethene using catalysts of titanium(IV) chloride (TiCl₄) and aluminium alkyls (e.g. triethylaluminium, Al(C₂H₅)₃). The process was introduced in 1953 by the German chemist Karl Ziegler (1898-1973). It allowed the manufacture of polythene at lower temperatures (about 60 °C) and pressures (about 1 atm) than used in the original process.

abrasion    →   abrazija

Abrasion (lat. abrasio - to scrape off) is a process of scraping or wearing down by friction.

activation energy    →   energija aktivacije

Activation energy (E_a) is the energy that must be added to a system in order for a process to occur, even though the process may already be thermodynamically possible. In chemical kinetics, the activation energy is the height of the potential barrier separating the products and reactants. It determines the temperature dependence on the reaction rate.

acylaction reaction    →   reakcije aciliranja

Acylaction reaction involves the introduction of an acyl group (RCO-) into a compound. An alkyl halide is reacted with an alcohol or a carboxylic acid anhydride e.g.

The introduction of an acetyl group (CH₃CO-) is acetylation, a process used for protecting -OH groups in organic synthesis.