CHEMISTRY GLOSSARY

Bunsen’s cell    →   Bunsenov članak

Bunsen’s cell is a primary cell devised by Robert W. Bunsen consisting of a zinc cathode immersed in dilute sulphuric acid and carbon anode immersed in concentrated nitric acid. The electrolytes are separated by a porous pot. The cell gives an e.m.f. of about 1.9 V.

burette    →   bireta

Burette is a graded glass pipe which on its lower side has a glass faucet by which it can drop a precise quantity of liquid. Inner diameter of a burette must be equal in its whole length, because the accuracy of volume measurement depends upon that. Burettes are primarily used in volumetric analysis for titration with standard solution reagent. Most often Schellbach’s burette is used, graded on 50 mL with division of scale on 0.1 mL. Every burette is calibrated on discharge. For serial determining automatic burettes are used.

Butler-Volmer equation    →   Butler-Volmerova jednadžba

Butler-Volmer equation is an activation controlled reaction, the one for which the rate of reaction is controlled solely by the rate of the electrochemical charge transfer process, which is in turn an activation-controlled process. This gives rise to kinetics that are described by the Butler-Volmer equation:

where i_o is exchange current density, η is overpotential (η = E - E_o), n is number of electrons, α_A is anodic transfer coefficient, and α_C is cathodic transfer coefficient

calendering    →   kalandriranje

Calendering is the process of forming materials to make a film/sheet by passing them through a series of hot rollers.

calomel electrode    →   kalomel elektroda

Calomel electrode is a type of half cell in which the electrode is mercury coated with calomel (Hg₂Cl₂) and the electrolyte is a solution of potassium chloride and saturated calomel. In the calomel half cell the overall reaction is

Table: Dependence of potential of calomel electrode upon temperature and concentration of KCl according to standard hydrogen electrode

calorimeter    →   kalorimetar

Calorimeter is an instrument used to measure the energy absorbed or released in a chemical reaction. It also used in determining specific heat.

capacitor    →   kondenzator

Capacitor is a device that stores electric charges. The symbol for a capacitor in electric circuit schemes is —| |—.

carbohydrate    →   ugljikohidrat

Carbohydrates (often called carbs for short) are polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis. They are also known as saccharides, a term derived from the Latin word saccharum for sugar. Carbohydrates are the most abundant class of compounds in the biological world, making up more than 50 % of the dry weight of the Earth’s biomass. Every type of food we eat can have its energy traced back to a plant. Plants use carbon dioxide and water to make glucose, a simple sugar, in photosynthesis. Other carbohydrates such as cellulose and starch are made from the glucose. Light from the sun is absorbed by chlorophyll and this is converted to the energy necessary to biosynthesize carbohydrates

The term carbohydrate was applied originally to monosaccharides, in recognition of the fact that their empirical composition can be expressed as C_x(H₂O)_y. Later structural studies revealed that these compounds were not hydrates but the term carbohydrate persists.

Carbohydrates are generally classed as either simple or complex. Simple sugars, or monosaccharides, are carbohydrates that can’t be converted into smaller subunits by hydrolysis. Complex carbohydrates are made of two (disaccharides) or more (oligosaccharides, polysaccharides) simple sugars linked together by acetal (glycosidic) bonds and can be split into the former by hydrolysis.

Carnot cycle    →   Carnotov kružni proces

Carnot cycle is the most efficient cycle of operations for a reversible heat engine. Published in 1824 by French physicist Nicolas Léonard Sadi Carnot (1796-1832), it consists of four operations on the working substance in the engine:

1-2: Isothermal expansion at thermodynamic temperature T₁ with heat Q_H taken in.

2-3: Adiabatic expansion with a fall of temperature to T₂.

3-4: Isothermal compression at temperature T₂ with heat Q_C given out.

4-1: Adiabatic compression at temperature back to T₁.

According to the Carnot principle, the efficiency of any reversible heat engine depends only on the temperature range through which it works, rather than the properties of the working substances.

catalyst    →   katalizator

Catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. Catalysts that have the same phase as the reactants are homogenous catalysts (e.g. enzymes in biochemical reactions). Those that have a different phase are heterogeneous catalyst (e.g. metals or oxides used in gas reactions).

The catalyst provides an alternative pathway by which the reaction can proceed, in which the activation energy is lower. In thus increases the rate at which the reaction comes to an equilibrium, although it does not alter the position of the equilibrium.