CHEMISTRY GLOSSARY

precipitate    →   precipitat

Precipitate or the deposit is an insoluble solid formed by reactions in a solution. For example, when a solution of silver nitrate is added to a solution of sodium chloride, insoluble silver chloride precipitates.

explosive    →   eksploziv

Explosive is a compound or mixture that, when ignited or detonated, undergoes rapid violent chemical reaction that produces large amount of gas and heat, accompanied by light, sound and a high pressure shock wave.

Faraday’s laws of electrolysis    →   Faradayevi zakoni elektrolize

Faraday’s laws of electrolysis are two laws found by British chemist and physicist Michael Faraday (1791-1867) in his experiments on electrolysis:

1. The quantity of matter extracted on the electrode is proportional to the quantity of charge (Q = I·t) which has flown in electrolysis time.

where z = number of electrons changed in reaction and F = Faraday’s constant which equals 96 487 C mol^-1.

2. The masses of the elements liberated by the same quantity of electricity are directly proportional to their chemical equivalents.

96 487 C will discharge 1 mol Ag and 1/2 mol Cu. The relevant half reactions are:

fission    →   fisija

Fission is a nuclear reaction in which an atomic nucleus breaks into smaller nuclei of comparable mass, releasing a large amount of energy.

product    →   produkt

Products are substances developed by chemical reactions from reactants.

racemisation    →   racemizacija

Racemisation is a conversion, by heat or by chemical reaction, of an optically active compound into an optically inactive form which half of the optically active substance becomes its miror image (enantiomer).

radical    →   radikal

Radical is a reaction intermediate where a bond is broken and the two parts of the molecule exist carrying a single unshared electron. The radicals are normally destroyed quickly by recombination or they break into another radical and a stable molecule.

fossil fuel    →   fosilno gorivo

Fossil fuels (coal, oil, and natural gas) are the fuels used by man as a source of energy. They are formed from the remains of living organisms and all have a high carbon or hydrogen content. They have value as fuels on the exothermic oxidation of carbon to form carbon dioxide

and the oxidation of hydrogen to form water

free radical    →   slobodni radikal

Free radical is a molecular fragment having one or more unpaired electrons, usually short-lived and highly reactive. They can be produced by photolysis or pyrolysis in which a bond is broken without forming ions. In formulas, a free radical is conventionally indicated by a dot (·CH₃, ·SnH₃, ·Cl). Free radicals are known to be formed by ionising radiation and thus play a part in deleterious degradation effects that occur in irradiated tissue. They also act as initiators or intermediates in oxidation, combustion, photolysis, and polymerisation.

fuel cell    →   gorivi članak

Fuel cell is a device that converts chemical energy into electrical energy. It is different from a battery in that the energy conversion continues as long as fuel and oxidising agent are fed to the fuel cell; that is, in principle indefinitely. (A battery is manufactured with a limited amount of chemicals, and it is exhausted when all the chemicals have reacted.) It is a galvanic cell where spontaneous chemical reactions occur at the electrodes. The fuel is oxidised at the anode, and the oxidising agent (almost always oxygen or air) is reduced at the cathode. Presently, the most commonly used fuel is hydrogen. More conventional fuels (e.g., petrol or natural gas) must be converted (reformed) into hydrogen before they can be utilised in a fuel cell.

Some fuel cells employ an aqueous solution as electrolyte, that can be either acidic or basic (alkaline), or an ion-exchange membrane soaked in aqueous solution can act as the electrolyte. These fuel cells operate at relatively low temperatures (from room temperature to not much above the boiling point of water). Some fuel cells employ molten salts (especially carbonates) as electrolytes and have to operate at temperatures of several hundred degrees centigrade (Celsius). Others employ ionically conductive solids as electrolyte and must operate close to 1 000 °C.