CHEMISTRY GLOSSARY

system    →   sustav

System is the region under consideration, as distinguished from the rest of the universe (the environment). Systems may be separated from environments by boundaries that prevent the transfer of mass (a closed system), of heat (an adiabatic system), or of any energy (an isolated system). Systems that exchange mass with the environment are open systems.

fat    →   mast

Fats are esters of glycerol and long chain carboxylic acids. Fats occur widely in plants and animals as a means of storing food energy, having twice the calorific value of carbohydrates. Fats derived from plants and fish generally have a greater proportion of unsaturated fatty acids than those from mammals. Fats may be either solid or liquid at room temperature, depending on their structure and composition. Unsaturated fats are liquid at room temperature.

Plant oils may be hardened by the addition of hydrogen atoms, converting double bonds to single bonds. This process is known as hydrogenation. Hydrogenated vegetable oils are often present in margarine and other processed foods.

Alkali hydrolysis of fat with sodium hydroxide it gives glycerol and soap (i.e. a mixture of the sodium salts of the fatty acids).

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.

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

freon    →   freon

Freon (chlorofluorocarbon, CFC) a type of compound in which some or all of the hydrogen atoms of hydrocarbon (usually an alkane) have been replaced by chlorine and fluorine atoms. Most CFC are chemically uncreative and are stable at high temperatures. They are used as aerosol propellants, refrigerants, and solvents, and in the manufacture of rigid packaging foam. CFC because of their chemical inertness, can diffuse unchanged into the upper atmosphere. Here, photochemical reactions cause them to break down and react with ozone. For his reason, their use has been discouraged.

temperature    →   temperatura

Temperature is a measure to the average kinetic energy of its molecules. The SI unit in which thermodynamic temperature is expressed is the kelvin (K).

thermit welding    →   termitno zavarivanje

Thermit welding is a group of welding processes in which fusion is produced by heating with superheated liquid metal resulting from a chemical reaction between a metal oxide and aluminium.

thermodynamic equilibrium    →   termodinmička ravnoteža

Thermodynamic equilibrium is a system equilibrium in which energy that it gains from its surroundings is exactly balanced by the energy that it loses, no matter how much time is allowed to pass.

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.

gamma radiation    →   gama-zračenje

Gamma radiation is electromagnetic radiation of extremely short wavelength. Gamma radiation ranges in energy from about 10^-15 J to 10^-10 J (10 keV to 10 MeV) (wavelength less than about 1 pm). Gamma rays are emitted by excited atomic nuclei during the process of passing to a lower excitation state.

Gamma rays are extremely penetrating and are absorbed by dense materials like lead and uranium. Exposure to gamma radiation may be lethal.