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.

Helmholz free energy    →   Helmholzova slobodna energija

Helmholz free energy (A) is a thermodynamic function defined by A = U - TS, where U is the internal energy, S the entropy, and T the thermodynamic temperature. For a reversible isothermal process ΔA represents the useful work available.

ion exchange    →   ionska izmjena

Ion exchange is a process involving the adsorption of one or several ionic species accompanied by the simultaneous desorption (displacement) of one or more other ionic species.

decomposition    →   raspadanje

Decomposition occurs when chemical compounds are broken up into simple molecules, and even as far as their original elements. These processes are normally irreversible. An example of decomposition is when ammonium nitrate is heated. This produces nitrous oxide and water which are unable to recombine.

desiccant dryers    →   sredstva za sušenje

Desiccant dryers (air dryers) use nonconsumable chemicals such as silica gel or active alumina, and can remove almost all the moisture from compressed air by adsorbing moisture on its surface. The method of regeneration, the process of removing adsorbed water from the desiccant, is the primary distinguishing feature among the various types of desiccant dryers. There are three ways to regenerate a desiccant: with air, internal or external heaters, or a heat pump.

diagenesis    →   dijageneza

Diagenesis is the process that turns sediments into sedimentary rocks. The lithification (literally turning into stone) of the sediments is usually accomplished by a cementing agent. How the weight of the overlying material increases the grains closer together, reducing pore space and eliminating some of the contained water. This water may carry mineral components in solution, and these constituents precipitate as new minerals in the pore spaces. This causes cementation, which will then start to bind the individual particles together. Further compaction and burial may cause recrystallization of the minerals to make the rock even harder.

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).

Mannich reaction    →   Mannichova reakcija

Mannich reaction is a process in which hydrogen atoms in organic compounds are replaced with a methyl group.

metabolism    →   metabolizam

Metabolism is a sum of all chemical and physiological processes by which the body builds and maintains itself. It is a process of building the body’s molecular structures from nutrients (anabolism) and breaking them down for energy (catabolism).

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