CHEMISTRY GLOSSARY

protein    →   bjelančevina

Proteins are natural organic compounds of animal or herbal origin, essential in diet. They are natural polymers developed from a crowd of interconnecting monomers of amino acids, with relative molecular masses amounting up to a few million.

purification    →   pročišćavanje

Purification is the physical or chemical process of removing contaminants from a compound. The physical processes may include sublimation, distillation, filtration, crystallisation, or extraction. The chemical processes may involve formation of a derivative, purification of the derivative and recovery of the original material in a pure form of the derivative.

Raman effect    →   Ramanov efekt

Raman effect is a type of scattering of electromagnetic radiation in which light suffers a change in frequency and a change in phase as it passes through a material medium. Named according to the Indian physicist C. V. Raman (1889-1970). The intensity of Raman scattering is about one-thousandth of that in Rayleigh scattering in liquids.

reverse reaction    →   povratna reakcija

Reverse reaction is a reaction in backward directions, reaction (in the reversible reaction) in which original reactants emerge again from a products. It goes from right to left.

equilibrium constant    →   konstanta ravnoteže

The equilibrium constant (K) was originally introduced in 1863 by Norwegian chemists C.M. Guldberg and P. Waage using the law of mass action. For a reversible chemical reaction represented by the equation

chemical equilibrium occurs when the rate of the forward reaction equals the rate of the back reaction, so that the concentrations of products and reactants reach steady-state values.

The equilibrium constant is the ratio of chemical activities of the species A, B, C, and D at equilibrium.

To a certain approximation, the activities can be replaced by concentrations.

For gas reactions, partial pressures are used rather than concentrations

The units of K_p and K_c depend on the numbers of molecules appearing in the stoichiometric equation (a, b, c, and d).

The value equilibrium constant depends on the temperature. If the forward reaction is exothermic, the equilibrium constant decreases as the temperature rises. The equilibrium constant shows the position of equilibrium. A low value of K indicates that [C] and [D] are small compared to [A] and [B]; i.e. that the back reaction predominates.

The equilibrium constant is related to Δ_rG°, the standard Gibbs free energy change in the reaction, by

Schiff base    →   Schiffova baza

Schiff base is a class of compounds derived by the chemical reaction (condensation) of aldehydes or ketones with aromatic amines, for example

They were named after the German chemist Hugo Schiff (1834-1915).

seaborgium    →   seaborgij

Seaborgium was discovered by workers at the Nuclear Institute at Dubna (USSR) and by workers at the University of California, Berkeley (USA) in 1974. Named in honour of Glenn T. Seaborg, American nuclear chemist and Nobel prize winner. It is synthetic radioactive metal. Seaborgium was made by bombarding californium-249 with oxygen-18.

Fajans’ rules    →   Fajansova pravila

Fajans’ rules, formulated by American chemist of Polish origin. Kazimierz Fajans (1887-1975), indicating the extent to which an ionic bond has covalent character caused by polarisation of the ions. Covalent character is more likely if:

1. the charge of the ions is high;

2. the positive ion is small or the negative ion is large;

3. the positive ion has an outer electron configuration that is not a noble- gas configuration.

Fischer-Tropsch process    →   Fischer-Tropschov postupak

Fischer-Tropsch process is an industrial method of making hydrocarbon fuels from carbon monoxide and hydrogen. The process was introduced in 1933. and used by Germany in World War II. to produce motor fuel. Hydrogen and carbon monoxide are mixed in the ratio 2:1 (water gas was used with added hydrogen) and passed at 200 °C over a nickel or cobalt catalyst. The resulting hydrocarbon mixture can be separated into a higher-boiling fraction for Diesel engines and a lower-boiling petrol fraction. The petrol fraction contains a high proportion of straight-chain hydrocarbons and has to be reformed for use in motor fuel. Alcohols, aldehydes, and ketones are also present. The process is also used in the manufacture of SNG from coal. It is named after the German chemist Franz Fischer (1852-1932) and the Czech Hans Tropsch (1839-1935).

fluorine    →   fluor

Fluorine was discovered by Henri Moissan (France) in 1886. The origin of the name comes from the Latin word fluere meaning to flow. It is pale yellow to greenish gas, with an irritating pungent odour. Extremely reactive, flammable gas. Reacts violently with many materials. Toxic by inhalation or ingestion. Does not occur uncombined in nature. Fluorine is found in the minerals fluorite (CaF₂) and cryolite (Na₃AlF₆). Electrolysis of hydrofluoric acid (HF) or potassium acid fluoride (KHF₂) is the only practical method of commercial production. Used in refrigerants and other fluorocarbons. Also in toothpaste as sodium fluoride (NaF).