CHEMISTRY GLOSSARY

Bohr atom    →   Bohrov atom

Bohr atom is a model of the atom that explains emission and absorption of radiation as transitions between stationary electronic states in which the electron orbits the nucleus at a definite distance. The Bohr model violates the Heisenberg uncertainty principle since it postulates definite paths and moment for electrons as they move around the nucleus. Modern theories usually use atomic orbitals to describe the behaviour of electrons in atoms.

chemical equation    →   kemijska jednadžba

Chemical equation is a way of denoting a chemical reaction using the symbol for the participating particles (atoms, molecules, ions, etc.); for example,

The single arrow is used for an irreversible reaction; double arrows are used for reversible reactions. When reactions involve different phases, it is usual to put the phase in brackets after the symbol.

The numbers a, b, c, and d, showing the relative numbers of molecules reacting, are called the stoichiometric coefficients. The convention is that stoichiometric coefficients are positive for reactants and negative for products. If the sum of the coefficients is zero, the equation is balanced.

chemical equation equalization    →   izjednačavanje kemijske jednadžbe

Chemical equation equalization is determining values of stechiometric coefficients of reactants and products in a chemical equation in a way that the number of atoms of each element is equal before and after the reaction.

D-lines    →   D-linije

D-lines are two close lines in the yellow region of the spectrum of sodium, having wavelengths 589.6 nm (D₁) and 589.0 nm (D₂). They were labeled as feature D in the solar spectrum by German optician Joseph von Fraunhofer (1787-1826). As they a prominent and easily recognized they are used as a standard in spectroscopy.

diatomaceous earth    →   dijatomejska zemlja

Diatomaceous earth is a naturally occurring siliceous sedimentary mineral compound from microscopic skeletal remains (frustules) of diatoms, unicellular aquatic plants of microscopic size. Their fossilized remains are called diatomite and contains approximately 3000 diatom frustules per cubic millimetre.

Diatomite is relatively inert and has a high absorptive capacity, large surface area, and low bulk density. It consists of approximately 90 % silica, and the remainder consists of compounds such as aluminum and iron oxides. The fine pores in the diatom frustules make diatomite an excellent filtering material for waters, beverages, oils, chemicals, as well as many other products.

equation of state    →   jednadžba stanja

Equation of state is an equation relating the pressure, volume, and temperature of a substance or system. Equation of state for ideal gas

where p is pressure, V molar volume, T temperature, and R the molar gas constant (8.314 JK^-1mol^-1).

Fick’s law    →   Fickov zakon

Fick’s law is the statement that the flux J of a diffusing substance is proportional to the concentration gradient, i.e.,

where D is called the diffusion coefficient.

gravimetrical factor    →   gravimetrijski faktor

Gravimetrical factor is stechiometric proportion between molar mass of analyte and molar mass of precipitate in gravimetry.

gravimetry    →   gravimetrija

Gravimetry is the quantitative measurement of an analyte by weighing a pure, solid form of the analyte. Since gravimetric analysis is an absolute measurement, it is the principal method for analysing and preparing primary standards.

A typical experimental procedure to determine an unknown concentration of an analyte in a solution is as follows:

- quantitatively precipitate the analyte from the solution

- collect the precipitate by filtering and wash it to remove impurities

- dry the solid in an oven to remove the solvent

- weigh the solid on an analytical balance

- calculate the analyte concentration in the original solution based on the weight of the precipitate.

heat capacity    →   toplinski kapacitet

Heat capacity is defined in general as dQ/dT, where dQ is the amount of heat that must be added to a system to increase its temperature by a small amount dT. The heat capacity at a constant pressure is C_p = (∂H/∂T)_p; that at a constant volume is C_V = (∂E/∂T)_V, where H is enthalpy, E is internal energy, p is pressure, V is volume, and T is temperature. An upper case C normally indicates the molar heat capacity, while a lower case c is used for the specific (per unit mass) heat capacity.