CHEMISTRY GLOSSARY

phase    →   faza

Phase is a portion of a physical system (solid, liquid, gas) that is homogeneous throughout, has definable boundaries, and can be separated physically from other phases.

angular acceleration    →   kutna akceleracija

If the angular velocity of a body changes from an initial value ω_i to a final value ω_f, average angular acceleration, α, can be defined for the time interval Δt = t_f - t_i:

The instantaneous angular acceleration, α, is the limit of the average angular acceleration, as Δt is made to approach zero:

SI unit for angular acceleration is s^-2.

atom radius    →   radijus atoma

Atoms and molecules have no strict boundaries. The volume of a free atom is usually defined as that volume that contains 90 % of electron cloud. The radius of an atom represents half of interatom distance of two identical atoms which are in touch but are not interconnected either by a covalent or an ionic bond, but with a very weak van der Waals’s bond.

Charles’ law    →   Charlesov zakon

The volume of a fixed mass of gas at a constant pressure expand by the constant fraction of its volume at 0 °C. For each Celsius or kelvin degree its temperature is raised. For any ideal gas fraction it is approximately 1/273. This can be expressed by the equation

were V° is the volume at 0°C and V is its volume at t°C.

This is equivalent to the statement that the volume of a fixed mass of gas at a constant pressure is proportional to its thermodynamic temperature

This law also know as Gay-Lussac’s law.

An equation similar to the one given above applies to pressures for ideal gases:

system    →   sustav

System is the region under consideration, as distinguished from the rest of the universe (the environment). Systems may be separated from environments by boundaries that prevent the transfer of mass (a closed system), of heat (an adiabatic system), or of any energy (an isolated system). Systems that exchange mass with the environment are open systems.

angular velocity    →   kutna brzina

A point-like object that undergoes circular motion changes its angular position from initial Θ_i to final Θ_f, relative to a fixed axis, specified in a coordinate system with an origin that coincides the centre of the circular path of object. The change in its angular position is called angular displacement ΔΘ = Θ_f - Θ_i. Also, a rigid body that rotates about a specified rotation axis, changing its angular position from initial Θ_i to final Θ_f, undergoes an angular displacement ΔΘ.

The average angular velocity, ω_av, is the ratio of the angular displacement and the time interval Δt=t_f-t_i, in which that displacement occurs.

Θ_f and Θ_i are the initial and final angular position, respectively.

The instantaneous angular velocity ω is the limit of the average angular velocity, as Δt is made to approach zero.

ω_av and ω are positive for the counterclockwise rotation (in direction of increasing Θ) and negative for the clockwise rotation (in direction of decreasing Θ).

SI unit for angular velocity is s^-1.The measure for the angle Θ is radian. The relationship between radians and degrees is:

For example, the angular velocity of the minute hand of a clock is:

zeta potential    →   zeta potencijal

Zeta potential (ζ) is the potential across the interface of all solids and liquids. Specifically, the potential across the diffuse layer of ions surrounding a charged colloidal particle, which is largely responsible for colloidal stability. Also called electrokinetic potential.

distilled water    →   destilirana voda

Distilled water is water purified by distillation so as to free it from dissolved salts and other compounds. Distilled water in equilibrium with the carbon dioxide in the air has conductivity of about 0.8×10^-6 S cm^-1. Repeated distillation in vacuum can bring conductivity down to 0.043×10^-6 S cm^-1 at 18 °C. The limiting conductivity is due to self ionisation

Hooke’s law    →   Hookeov zakon

Hooke’s law stating that the deformation of a body is proportional to the magnitude of the deforming force, provided that the body’s elastic limit (see elasticity) is not exceeded. If the elastic limit is not reached, the body will return to its original size once the force is removed. The law was discovered by English physicist Robert Hooke in 1676.

If a body on elastic spring is displaced from its equilibrium position (i.e. if the spring is stretched or compressed), a restitution force tries to return the body back in its equilibrium position. The magnitude of that force is proportional to the displacement of the body

Where F is the restitutional (elastic) force, x is the displacement of the body and k is the spring constant, which depends on dimensions, shape and material of the spring.

Ilkovic equation    →   Ilkovičeva jednadžba

Ilkovic equation is a relation used in polarography relating the diffusion current (i_d) and the concentration of the depolarizer (c), which is the substance reduced or oxidized at the dropping mercury electrode. The Ilkovic equation has the form

Where k is a constant which includes Faraday constant, π and the density of mercury, and has been evaluated at 708 for max current and 607 for average current, D is the diffusion coefficient of the depolarizer in the medium (cm²/s), n is the number of electrons exchanged in the electrode reaction, m is the mass flow rate of Hg through the capillary (mg/sec), and t is the drop lifetime in seconds, and c is depolarizer concentration in mol/cm³.

The equation is named after the scientist who derived it, the Slovak chemist, Dionýz Ilkovič 1907-1980).