CHEMISTRY GLOSSARY

standard hydrogen electrode    →   standardna vodikova elektroda

Standard hydrogen electrode is a system in which hydrogen ion and gaseous hydrogen are present in their standard states. The convention is to designate the cell so that the standard hydrogen electrode is written first.

The electrode is used as a reference (of zero) for the values of other standard electrode potentials.

stoichiometric coefficient    →   stehiometrijski koeficijent

Stoichiometric coefficient (ν) is the number appearing before the symbol for each compound in the equation for a chemical reaction. By convention, it is negative for reactants and positive for products.

Stoichiometric coefficients describe the stoichiometry of the chemical reaction.

In this equation, a, b, c and d are called as Stoichiometric coefficients of the A, B, C and D respectively.

stoichiometry    →   stehiometrija

Stoichiometry is the relative proportions elements from compounds or in which substances react. Every chemical reaction has its characteristic proportions. For example, when methane unites with oxygen in complete combustion, 1 mol of methane requires 2 mol of oxygen.

At the same time, 1 mol of carbon dioxide and 2 mol of water are formed as reaction products.

Alternatively, 16 g of methane and 64 g of oxygen produce 44 g of carbon dioxide and 36 g of water.

The stoichiometric relationship between the products and reactants can be used to in calculations.

strontium    →   stroncij

Strontium was discovered by Sir Humphry Davy (England) in 1808. Named after the village of Strontian in Scotland. It is soft, malleable, silvery-yellow metal. Combustible in air, will react with water. Exposed surfaces form protective oxide film. Metal ignites and burns readily. Strontium is found in minerals celestite and strontianite. Used in flares and fireworks for crimson colour. Strontium-90 is a long lived highly radioactive fallout product of atomic-bomb explosions.

sucrose    →   saharoza

Sucrose (saccharose), or ordinary table sugar, is a disaccharide in which α-D-glucopyranose and β-D-fructofuranose are joined at their anomeric carbons by a glycosidic bond. There are no hemiacetals remaining in the sucrose and therefore sucrose is not a reducing sugar and does not exhibit mutarotation. Sugar is a white crystalline sweet compound found in many plants and extracted from sugar cane and sugar beet. It is used as a sweetening agent in food and drinks. If heated to 200 °C, sucrose becomes caramel. When sucrose is hydrolyzed it forms an equimolar mixture of glucose and fructose. This mixture of monosaccharides is called invert sugar. Honeybees have enzymes called invertases that catalyze the hydrolysis of sucrose. Honey, in fact, is primarily a mixture of glucose, fructose, and sucrose.

thermite    →   termit

Thermite is a stoichiometric powdered mixture of iron(II) oxide and aluminium for the reaction

The reaction is highly exothermic and the increase in temperature (over 2500 °C) is sufficient to melt the iron produced. It has been used for localized welding of steel object (e.g. railway lines) in the thermit process. Thermite is also used in incendiary bombs.

thermochemical equation    →   termokemijska jednadžba

Thermochemical equation is a compact equation representing a chemical reaction that describes both the stoichiometry and the energetics of the reaction. For example, the thermochemical equation

means When one mole of gaseous methane is burned in two moles of oxygen gas, one mole of carbon dioxide gas and 2 moles of steam are produced, and 2 220 kJ of heat are released.

thermosetting plastic    →   termostabilna plastika

Thermosetting plastics (thermosets) refer to a range of polymer materials that cure, through the addition of energy, to a stronger form. The energy may be in the form of heat (rubber), through a chemical reaction (two part epoxy), or irradiation. Thermoset materials are usually liquid or malleable prior to curing, and designed to be molded into their final form, or used as adhesive.

Thermoset polymer resins transformed into plastics or rubbers by cross-linking into a rigid, 3-D structure. A thermoset material cannot be melted and re-molded after it is cured.

van’t Hoff equation    →   van Hoffova jednadžba

Van’t Hoff equation is the equation expressing the temperature dependence on the equilibrium constant K of a chemical reaction:

where Δ_rH° is the standard enthalpy of reaction, R the molar gas constant, and T the temperature.

water ion product    →   ionski produkt vode

Water ion product (K_w) is a concentration product of hydrogen and hydroxide ions. For the reaction:

the equilibrium expression would be:

Note that all pure liquid terms are omitted, hence H₂O does not appear in the denominator. At 25 °C, K_w = 1.0×10^-14 mol²dm^-6 = (K_a)(K_b)