CHEMISTRY GLOSSARY

cryogenic fractionation    →   kriogena frakcinacija

Cryogenic fractionation is a process of separation of gases by cooling them until they enter their liquid state. Large scale gas production companies use this method to produce liquid oxygen, liquid nitrogen etc. Gases have different boiling points (the temperature at which they change from liquid to gas). Oxygen has a boiling point of -183 °C, and nitrogen a boiling point of -195.8 °C. Therefore by cooling the gas mixture to -183 °C, the oxygen can be collected as liquid and the nitrogen remains its gaseous form.

Dalton’s law    →   Daltonov zakon

Dalton’s law of partial pressure says that the total pressure eof gaseous mixture is equal to the sum of all gases partial pressures which make that mixture on the condition that they do not interact.

For example, if dry oxygen gas at 900 hPa is saturated with water vapor at 56 hPa, the pressure of the wet gas is 956 hPa.

Dewar flask    →   Dewarova posuda

Dewar flask or vacuum bottle is a container for storing hot or cold substances. It consists of two flasks, one placed inside the other, with a vacuum between. The vacuum prevents the conduction of heat from one flask to the other. For greater efficiency the flasks are silvered to reflect heat. The substance to be kept hot or cold, e.g., liquid air, is contained in the inner flask. The flask is named after British chemist and physicist Sir James Dewar (1842-1923). Dewar invented the Dewar flask in 1892 to aid him in his work with liquid gases. The common thermos bottle is an adaptation of the Dewar flask.

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.

flashback    →   uskakanje plamena

Flashback occurs when the flame in a gas torch burns back into the torch or hose; this is often accompanied by a hissing or squealing sound, and a pointed or smoky flame.

fluid mechanics    →   mehanika fluida

Fluid mechanics is the study of various properties of the fluid (liquids and gases): velocity, pressure, density and temperature, as functions of space and time.

gunpowder    →   barut

Gunpowder (black powder) is a low explosive composed of potassium nitrate, sulphur and charcoal. Typical proportions are 6:1:1.

heat of sublimation    →   toplina sublimacije

Heat of sublimation or enthalpy of sublimation is the energy required to convert one mole of a substance from the solid to the gas state (sublimation) without the appearance of the liquid state.

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).

dissociation    →   disocijacija

Dissociation is the process by which a chemical combination breaks up into simpler constituents as a result of either added energy (dissociated by heat), or the effect of a solvent on a dissolved polar compound (electrolytic dissociation). It may occur in the gaseous, solid, or liquid state, or in a solution.

An example of dissociation is the reversible reaction of hydrogen iodide at high temperatures

The term dissociation is also applied to ionisation reactions of acids and bases in water. For example

which is often regarded as a straightforward dissociation into ions