CHEMISTRY GLOSSARY

diamagnetism    →   dijamagnetizam

In diamagnetism the magnetisation is in the opposite direction to that of the applied field, i.e. susceptibility is negative. It results from changes induced in the orbits of electrons in the atoms of a substance by the applied field, the direction of the change opposing the applied flux.

dielectric constant    →   dielektrična konstanta

Dielectric constant or permittivity (ε) is an index of the ability of a substance to attenuate the transmission of an electrostatic force from one charged body to another. The lower the value, the greater the attenuation. The standard measurement apparatus utilises a vacuum whose dielectric constant is 1. In reference to this, various materials interposed between the charged terminal have the following value at 20 °C:

The exceptionally high value for water accounts for its unique behaviour as a solvent and in electrolytic solutions. Dielectric constant values decrease as the temperature rises.

diffusion    →   difuzija

Diffusion is the spontaneous mixing of one substance with another when in contact or separated by a permeable membrane. Diffusion is a result of the random motions of their component atoms, molecules, ions, or other particles. Diffusion occurs most readily in gases, less so in liquids, and least in solids. The rate of diffusion is proportional to the concentration of the substance and increases with temperature. The theoretical principles are stated in Fick’s laws.

dioxin    →   dioksin

Dioxin is a general term that describes a group of hundreds of chemicals that are highly persistent in the environment. The most toxic compound is 2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD. The toxicity of other dioxins and chemicals like PCBs that act like dioxin are measured in relation to TCDD. Dioxin is formed as an unintentional by-product of many industrial processes involving chlorine such as waste incineration, chemical and pesticide manufacturing and pulp and paper bleaching. Dioxin was the primary toxic component of Agent Orange, found at Love Canal in Niagara Falls, NY and was the basis for evacuations at Times Beach, MO and Seveso, Italy.

Dioxin is formed by burning chlorine-based chemical compounds with hydrocarbons. The major source of dioxin in the environment comes from waste-burning incinerators of various sorts and also from backyard burn-barrels. Dioxin pollution is also affiliated with paper mills which use chlorine bleaching in their process, with the production of Polyvinyl Chloride (PVC) plastics, and with the production of certain chlorinated chemicals (like many pesticides).

dipole moment    →   dipolni moment

Electric dipole moment (μ) is a product of the positive charge and the distance between the charges. Dipole moments are often stated in debyes; The SI unit is the coulomb metre. In a diatomic molecule, such as HCl, the dipole moment is a measure of the polar nature of the bond; i.e. the extent to which the average electron charges are displaced towards one atom (in the case of HCl, the electrons are attracted towards the more electronegative chlorine atom). In a polyatomic molecule, the dipole moment is the vector sum of the dipole moments of the individual bonds. In a symmetrical molecule, such as tetrafluoromethane (CF₄) there is no overall dipole moment, although the individual C-F bonds are polar.

distillation    →   destilacija

Distillation is a process of boiling a liquid and condensing and collecting the vapour. The liquid collected is the distillate. The usual purpose of distillation is purification or separation of the components of a mixture. This is possible because the composition of the vapour is usually different from that of liquid mixture from which it is obtained. Petrol, kerosene, fuel oil, and lubricating oil are produced from petroleum by distillation.

distilled water    →   destilirana voda

Distilled water is water purified by distillation so as to free it from dissolved salts and other compounds. Distilled water in equilibrium with the carbon dioxide in the air has conductivity of about 0.8×10^-6 S cm^-1. Repeated distillation in vacuum can bring conductivity down to 0.043×10^-6 S cm^-1 at 18 °C. The limiting conductivity is due to self ionisation

electrochemical cell    →   elektrokemijski članak

Electrochemical cell is a device that converts chemical energy into electrical energy or vice versa when a chemical reaction is occurring in the cell. It consist of two electronically conducting phases (e.g., solid or liquid metals, semiconductors, etc) connected by an ionically conducting phase (e.g. aqueous or non-aqueous solution, molten salt, ionically conducting solid). As an electric current passes, it must change from electronic current to ionic current and back to electronic current. These changes of conduction mode are always accompanied by oxidation/reduction reactions.

An essential feature of the electrochemical cell is that the simultaneously occurring oxidation-reduction reactions are spatially separated. E.g., in a spontaneous chemical reaction during the oxidation of hydrogen by oxygen to water, electrons are passed directly from the hydrogen to the oxygen.

In contrast, in the spontaneous electrochemical reaction in a galvanic cell the hydrogen is oxidised at the anode by transferring electrons to the anode and the oxygen is reduced at the cathode by accepting electrons from the cathode. The ions produced in the electrode reactions, in this case positive hydrogen ions and the negative hydroxyl (OH^-) ions, will recombine in the solution to form the final product of the reaction: water. During this process the electrons are conducted from the anode to the cathode through an outside electric circuit where the electric current can drive a motor, light a light bulb, etc. The reaction can also be reversed: water can be decomposed into hydrogen and oxygen by the application of electrical power in an electrolytic cell.

electrogravimetry    →   electrogravimetrija

Electrogravimetry is an electroanalytical technique in which the substance to be determined (usually a metal) is deposited out on an electrode which is weighed before and after the experiment. The potential of the electrode must be carefully chosen to ensure that only the metal do be determined will deposit.

electrolytes    →   elektroliti

Electrolytes are substances which, when melted or dissolved in water, conduct electric current. By melting or dissolving they are dissociated into electrically charged particles (ions) which are able to conduct electric current. By passing of electric current the transfer of matter occurs. Positively charged particles (cations) travel towards the negative pole (the cathode) and negatively charged particles (the anions) travel towards the positive pole (the anode). Liquid metals, in which the conduction is by free electrons, are not usually regarded as electrolytes. Solid conductors of ions, as in the sodium-sulphur cell, are also known as electrolytes. Depending upon how it conducts electric current, matter can be divided into strong electrolytes, weak electrolytes and nonconductors.