CHEMISTRY GLOSSARY

vapour    →   para

Vapour is the gaseous state of some matter which can be converted into liquid when exposed to pressure.

Joule-Thomson’s effect    →   Joule-Thomsonov efekt

Temperature of ideal gas will not be changed when it is repressed to a lower pressure, but when real gases are repressed to a lower pressure, a lower or higher temperature change appears under high pressures. The temperature change which appears at real gas expansion in a system into which energy is not brought is called Joule-Thomson’s effect. It was determined that when air is repressed by 1 bar, its temperature drops by 0.25 °C. That minute effect is completely irrelevant for most technical processes, but is also used in gas liquefying procedure.

kinetic energy    →   kinetička energija

Kinetic energy (E_k) is associated with the state of motion of a body. It is a scalar property and defined to be

Kinetic energy is most clearly exhibited in gases, in which molecules have much greater freedom of motion than in liquids and solids.

law of conservation of mass    →   zakon o očuvanju mase

Law of conservation of mass states that no detectable gain or loss in mass occurs in chemical reactions. The state of a substance may change in a chemical reaction, for example, from a solid to a gas, but its total mass will not change. Note that the energy released (exothermic) or adsorbed (endothermic) in a chemical reaction is a result of energy transfer between atoms and their environment.

plasma    →   plazma

Plasma is a highly ionised gas in which the charge of the electrons is balanced by the charge of the positive ions, so that the system as a whole is electrically neutral. Plasmas are created by exposing gases at low pressure to an electric or electromagnetic field. In semiconductor processing, plasmas are used for etching and thin film deposition (the excited state of the gas makes it very reactive). In everyday life plasmas are used to give light in fluorescent light bulbs, neon lamps, and blue insect traps.

saturated solution    →   zasićena otopina

Saturated solution is a solution that holds the maximum possible amount of dissolved material. When saturated, the rate of dissolving solid and that of recrystallisation solid are the same, and a condition of equilibrium is reached. The amount of material in solution varies with temperature; cold solutions can hold less dissolved solid material than hot solutions. Gases are more soluble in cold liquids than in hot liquids.

U-tube manometer    →   U-manometar

U-tube manometer contains water or mercury in a U-shaped tube, and is usually used to measure gas pressure. One end of the U tube is exposed to the unknown pressure field (P) and the other end is connected to a reference pressure source (usually atmospheric pressure) (P_ref), shown in the schematic below.

If fluid C is the atmosphere, fluid B is the liquid in the U tube (e.g. water or mercury), and fluid A is a gas, then we can assume that ρB >> ρA, ρC. The pressure contributed by the weight of gas within the U tube can therefore be neglected. The gage pressure of the gas can be approximated by,

abundance of elements    →   rasprostranjenost elemenata

Elements in nature are mostly found in different compounds and, rarely, in the free (elementary) state. In Earth’s crust the most abundant of all elements is oxygen (with 49.5 %), then silicon (25 %), aluminium (7.5 %), iron (4.7 %), calcium (3.4 %), sodium (2.6 %), potassium (2.4 %), magnesium (1.9 %) and hydrogen (1.9 %). These nine elements make up almost 99 % of the Earth’s composition.

acetylene    →   acetilen

Acetylene (ethyne) is a colourless unstable gas, C₂H₂, with a characteristic sweet odour. It is lighter than air, easily soluble in acetone (propanone) and it is explosive under high pressure.

activity coefficient    →   koeficijent aktiviteta

Activity coefficient (γ or f) is a fractional number which, when multiplied by the molar concentration of a substance in solution, yields the chemical activity. This term gives an idea of how much interaction exists between molecules at higher concentration.

In solutions of very low ionic strength, when m is less than 0.01, the Debye-Hückel limiting law can be used to calculate approximate activity coefficients

where γ_i = activity coefficient of the species i, z_i = charge on the species i and μ = ionic strength of the solution.