CHEMISTRY GLOSSARY

Soxhlet extractor    →   Soxhletov ekstraktor

Soxhlet extractor is a laboratory apparatus designed to extract substances with a low solubility in the extracting solvent. The method described by the German chemist Franz von Soxhlet (1848-1926) in 1879 is the most commonly used example of a semi-continuous method applied to extraction of lipids from foods. In the Soxhlet extractor, the sample soaks in hot solvent that is periodically siphoned off, distilled and returned to the sample. During each cycle, a portion of the non-volatile compound dissolves in the solvent. After many cycles the desired compound is concentrated in the distillation flask. The solvent in the flask is then evaporated and the mass of the remaining lipid is measured.

superfluid helium    →   superfluidni helij

Superfluidity in helium-4 was discovered in 1938 by the Soviet physicist Pyotr Leonidovich Kapitsa. Helium-4 exhibits superfluidity when it is cooled below 2.18 K (-270.97 C), which is called the lambda (λ) point. At these temperatures, helium-4 exhibits the characteristics of two distinct fluids, one of which appears to flow without friction. An extensive series of experiments showed that in this state of helium, called helium II (He II), there is an apparent enormous rise in heat conductivity, at an increase rate of about three million. Another unusual property of He II is its mobile, rapid flow through capillaries or over the rim of its containment vessel as a thin film that exhibits no measurable viscosity and appears unaffected by the forces of gravity or evaporation and condensation.

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.

thermodynamic laws    →   termodinamički zakoni

Thermodynamic laws are the foundation of the science of thermodynamics:

First law: The internal energy of an isolated system is constant; if energy is supplied to the system in the form of heat dq and work dw, then the change in energy dU = dq + dw.

Second law: No process is possible in which the only result is the transfer of heat from a reservoir and its complete conversion to work.

Third law: The entropy of a perfect crystal approaches zero as the thermodynamic temperature approaches zero.

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.

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.

wire mesh    →   azbestna mrežica

Wire mesh (wire gauze) is used for uniform distribution of flame heat in base of a heated body. It is made of a iron wire strands with or without ceramic interior cores.