CHEMISTRY GLOSSARY

thermodynamics    →   termodinamika

Thermodynamics is the scientific study of the interconversion of heat and other forms of energy.

Hesse’s law    →   Hessov zakon

Hesse’s law says that reaction heat of some chemical change does not depend on the way in which the reaction is conducted, but only on starting and ending system state. Hesse’s law is also known as the law of constant heat summation. Hesse’s law is also known as the law of constant heat summation. The law was first put forward in 1840 by the Swiss-born Russian chemist Germain Henri Hess (1802-1850).

Hesse’s law can be used to obtain thermodynamic data that cannot be measured directly. For example, it is very difficult to control the oxidation of graphite to give pure CO. However, enthalpy for the oxidation of graphite to CO₂ can easily be measured. So can the enthalpy of oxidation of CO to CO₂. The application of Hess’s law enables us to estimate the enthalpy of formation of CO.

The equation shows the standard enthalpy of formation of CO to be -110 kJ/mol.

hydrolysis    →   hidroliza

Hydrolysis is a chemical reaction in which water reacts with another substance to form two or more new substances. This involves ionisation of the water molecule, as well as splitting of the compound hydrolysed, e.g.

Examples are conversion of starch to glucose by water in the presence of suitable catalysts and a reaction of the ions of a dissolved salt to form various products, such as acids, complex ions, etc.

toxic chemical    →   bojni otrov

Toxic chemical means any chemical which through its chemical action on life processes can cause death, temporary incapacitation, or permanent harm to humans or animals. This includes all such chemicals, regardless of their origin or of their method of production, and regardless of whether they are produced in facilities, in munitions or elsewhere.

valence bond    →   valentna veza

In the valence bond theory, a valence bond is a chemical bond formed by overlap of half-filled atomic orbitals on two different atoms.

valence shell    →   valentna ljuska

Valence shell is the shell corresponding to the highest value of principal quantum number in the atom. The valence electrons in this shell are on average farther from the nucleus than other electrons. They are often directly involved in chemical reaction.

indicator    →   indikator

Indicator is a substance used to show the presence of a chemical substance or ion by its colour. Acid-base indicators are compounds, such as phenolphtaleine and methyl orange, which change colour reversibly, depending on whether the solution is acidic or basic. Oxidation-reduction indicators are substances that show a reversible colour change between oxidised and reduced forms.

krypton    →   kripton

Krypton was discovered by Sir William Ramsay and Morris W. Travers (England) in 1898. The origin of the name comes from the Greek word kryptos meaning hidden. It is colourless, odourless rare noble gas. Reacts only with fluorine. Krypton is obtained from production of liquid air. Used in lighting products. Some is used as inert filler-gas in incandescent bulbs. Some is mixed with argon in fluorescent lamps. The most important use is in flashing stroboscopic lamps that outline airport runways.

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.

luminescence    →   luminiscencija

Luminescence (from Latin lumen, light) is the emission of electromagnetic radiation (UV, visible or IR) from atoms or molecules as a result of the transition of an electronically excited state to a lower energy state, usually the ground state. Luminescence can be divided into categories by duration (fluorescence or phosphorescence) or by the mechanism that creates the light (radioluminescence, electroluminescence, photoluminescence, thermoluminescence, triboluminescence, chemiluminescence, bioluminescence). The prefix identifies the energy source responsible for generating or releasing the light.

Phosphorescence is emission of light from a substance exposed to radiation and persisting as an afterglow after the source of excitation has been removed. Fluorescence, on the other hand, is an almost instantaneous effect, ending within about 10^-8 second after excitation.