CHEMISTRY GLOSSARY

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.

sacrificial protection    →   zaštita žrtvovanom elektrodom

Sacrificial protection is the protection of iron or steel against corrosion by using a more reactive metal. Pieces of zinc or magnesium alloy are attached to pump bodies and pipes. The protected metal becomes the cathode and does not corrode. The anode corrodes, thereby providing the desired sacrificial protection. These items are known as sacrificial anodes and "attract" the corrosion to them rather than the iron/steel. The sacrificial anodes must be replaced periodically as they corrode.

The iron pipe will be connected to a more reactive metal such as magnesium through cooper wires, the magnesium will donate its electrons to the iron preventing it from rusting. Iron which is oxidises will immediately be reduced back to iron.

saturated fat    →   zasićena mast

Saturated fats are fats in foods that are solid at room temperature. They come chiefly from animal sources (beef, whole-milk dairy products, dark meat poultry) but also from tropical vegetable oils (coconut, palm).

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.

second    →   sekunda

Second (s) is the SI base unit of time.

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels (F = 4, m_F = 0 to F = 3, m_F = 0) of the ground state of the caesium 133 atom.

sulfur    →   sumpor

Sulfur has been known since ancient times. The origin of the name comes from the Sanskrit word sulvere meaning sulphur; also from the Latin word sulphurium meaning sulphur. It is pale yellow, odourless, brittle solid, which is insoluble in water but soluble in carbon disulfide. Sulfur is found in pure form and in ores like cinnabar, galena, sphalerite and stibnite. Pure form is obtained from underground deposits by the Frasch process. Used in matches, gunpowder, medicines, rubber and pesticides, dyes and insecticides. Also for making sulfuric acid (H₂SO₄).

supercritical carbon dioxide    →   superkritični ugljikov dioksid

Supercritical carbon dioxide (scCO₂) is a powerful, cheap, non-toxic and environmental friendly solvent. When used at a supercritical state (over 74 bar and 31 °C), it achieves similar solvating power as its organic competitors, such as hydrocarbons and chlorinated solvents. Supercritical carbon dioxide is one of few solvents that can be unrestrictedly used for food processing.

Tafel plot    →   Tafelov dijagram

Tafel plot is the graph of the logarithm of the current density j against the overpotential η in electrochemistry in the high overpotential limit. An electrode when polarised frequently yields a current potential relationship over a region which can be approximated by:

where η is change in open circuit potential, i is the current density, B and i₀ is constants. B is known as the Tafel Slope. If this behaviour is observed a plot of the semilogarithmic components is known as the Tafel line and the diagram is called the Tafel diagram.

thermal expansion    →   toplinsko rastezanje

Thermal expansion is a change in dimensions of a material resulting from a change in temperature. All objects change size with changes in temperature. The change ΔL in any linear dimension L is given by

in which α is the thermal coefficient of linear expansion, L_o is the initial or reference dimension at temperature T_o (reference temperature) and ΔT is change in temperature which causes the change in dimension.

The change ΔV in the volume of a sample of solid or liquid is

Here γ is coefficient of volume expansion, V_o is the volume of the sample at temperature T_o and ΔV is the change in volume over the temperature range ΔT. With isotropic substances, the coefficient of volume expansion can be calculated from the coefficient of linear expansion: γ = 3α.

thermometer    →   termometar

Thermometers are devices for measuring temperature. Linear and volume thermal expansion are macroscopic properties of matter, which can be easily measured, relative to measurements of microscopic properties, on the basis of which, temperature is defined. Thermometers based on thermal expansion are secondary instruments that is, they have to be calibrated in comparison to a standard thermometer. In a thermometer with liquid, mercury or alcohol is placed in a small glass container. If temperature increases, the liquid undergoes volume expansion and rises in a capillary. The level of the raised liquid is the measure of temperature. Mercury thermometers measure temperatures in the temperature range between -39 °C and 300 °C. Alcohol thermometers measure lower temperatures. Bimetal thermometers have a spiral spring, which consists of two metals with different coefficients of linear expansion. When temperature changes, metals undergo different change in length and the consequence twisting of the spring is transferred to a pointer, the deflection of which is the measure of temperature.