CHEMISTRY GLOSSARY

surface tension    →   površinska napetost

Surface tension (σ) is a property of liquids arising from unbalanced molecular cohesive forces at or near the surface, as a result of which the surface tends to contract and has properties resembling those of a stretched elastic membrane. As a result of which the surface tends to contract and has properties resembling those of a stretched elastic membrane.

activator    →   aktivator

Activator is a substance that increases the activity of a catalyst; for example, a substance that - by binding to an allosteric site on an enzyme - enables the active site of the enzyme to bind to the substrate.

activity    →   aktivitet

Activity (a) is a thermodynamic function used in place of concentration in equilibrium constants for reactions involving nonideal gases and solutions. For the species i activity is defined as

where a_i is the activity of the species i, c_i is its molar concentration, and f_i is a dimensionless quantity called the activity coefficient.

allotrope    →   alotrop

Allotropes are the elements which exist in two or more different forms in the same physical state. Allotropes generally differ in physical properties and may also differ in chemical activity.

Diamond, graphite and fullerenes are three allotropes of the element carbon. Graphite is a soft, black, slippery substance; by contrast, diamond is one of the hardest substances known. The different properties of the allotropes arise from their chemical structures. Diamonds typically crystallize in the cubic crystal system and consist of tetrahedrally bonded carbon atoms. Graphite crystallizes in the hexagonal system. In the fullerenes, the carbon atoms taking the form of a hollow sphere, ellipsoid, or tube.

In some cases, the allotropes are stable over a temperature range, with a definite transition point at which one changes into the other. For instance, tin has two allotropes: white (metallic) tin stable above 13.2 °C and grey (nonmetallic) tin stable below 13.2 °C.

The term allotropes may also be used to refer to the molecular forms of an element. Ozone is a chemically active triatomic allotrope of the element oxygen.

detergent    →   deterdžent

Detergent is a substance added to water to improve its cleaning properties. Although water is a powerful solvent for many compounds, it will not dissolve grease and natural oils. Detergents are compounds that cause such nonpolar substances to go into solution in water. Soap is the original example, owing its action to the presence of ions formed from long-chain fatty acids ion (e.g. stearat ion, CH₃(CH₂)₁₆COO^-).

enzyme    →   enzim

Enzyme is a protein that acts as a catalyst in biochemical reactions. Each enzyme is specific to a particular reaction or a group of similar reactions. Many require the association of certain nonprotein cofactors in order to function. The molecule undergoing a reaction (the substrate) binds to a specific active site on the enzyme molecule to form a short-lived intermediate: this greatly increases (by a factor of up to 10²⁰) the rate at which the reaction proceeds to form the product.

law of chemical equilibrium    →   zakon o kemijskoj ravnoteži

Law of chemical equilibrium (also called the law of mass action) states that the rate at which a substance reacts is proportional to its active mass (i.e. to its molar concentration). Thus, the velocity of a chemical reaction is proportional to the product of the concentration of the reactants.

levorotatory    →   lijevokretan

Levorotatory is refers to an optically active substance that rotates the plane of plane polarised light counterclockwise.

poison    →   otrov

Poisons are substance, which upon contact or being introduced into an organism, impair or prevent normal metabolic processes from taking place, thus altering the normal functioning of organs or tissues.

Poisons are molecules or material that tends to collect on a catalyst surface, blocking access to active sites or destroying their activities.

Poisons are substance that can reduce a nuclear reaction by absorbing neutrons, thereby preventing more fission. If enough poisons are present in a reactor core, the chain reaction will die out.

polarimetry    →   polarimetrija

Polarimetry measures the overall turning of the flat of polarised light. It is used when analysing optically active substances and compounds.