CHEMISTRY GLOSSARY

universal gas constant    →   univerzalna plinska konstanta

Universal gas constant R has the value of 8.314 472(15) J K^-1 mol^-1. It corresponds to the volume work performed by one mole of gas heated by 1 K at standard pressure.

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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.

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Henry’s law    →   Henryjev zakon

Henry’s law was discovered in 1801 by the British chemist William Henry (1775-1836). At a constant temperature the mass of gas dissolved in a liquid at equilibrium is proportional to the partial pressure of the gas. It applies only to gases that do not react with the solvent.

where p_i is the partial pressure of component i above the solution, x_i is its mole fraction in the solution, and K_x is the Henry’s law constant (a characteristic of the given gas and solvent, as well as the temperature).

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ideal gas law    →   jednadžba stanja idealnog plina

The generalized ideal gas law is derived from a combination of the laws of Boyle and Charles. Ideal gas law is the equation of state

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

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Joule-Thomson’s effect    →   Joule-Thomsonov efekt

Temperature of ideal gas will not be changed when it is repressed to a lower pressure, but when real gases are repressed to a lower pressure, a lower or higher temperature change appears under high pressures. The temperature change which appears at real gas expansion in a system into which energy is not brought is called Joule-Thomson’s effect. It was determined that when air is repressed by 1 bar, its temperature drops by 0.25 °C. That minute effect is completely irrelevant for most technical processes, but is also used in gas liquefying procedure.

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kelvin    →   kelvin

Kelvin (K) is the SI base unit of thermodynamic temperature.

The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The unit was named after the British scientist Sir. W. Thompson, Lord Kelvin (1824-1907).

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vacuum distillation    →   vakuum destilacija

Vacuum distillation is distillation under reduced pressure. The depression in the boiling point of the substance distilled means that the temperature is lower, which may prevent the substance from decomposing.

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vapour    →   para

Vapour is the gaseous state of some matter which can be converted into liquid when exposed to pressure.

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Knudsen burette    →   Knudsenova bireta

Knudsen's automatic bulb-burette, developed by the Danish physicist Martin Knudsen (1871-1949), is designed in a way that even routine field analysis in a boat laboratory would provide highly accurate measurements. The burette is filled with a mixture of silver nitrate from reservoir R, located above the burette, by opening the A valve. When the solution crosses the three-way C valve the A valve is closed preventing further solution flow in to the burette. Any extra solution is caught in the W bowl. Turn the C valve, which marks the zero on the scale, in order to allow atmospheric air to enter the burette. Since most open-ocean samples lie in a relatively small chlorinity range, the burette is designed so that much of its capacity is in the bulb (B). This allows the titration to be quick (by quickly releasing contents from the B area) and reduces the error that occurs from the slow drainage along the inner wall of the burette.

Each millimeter is divided in to twenty parts (double millimeter division of the Knudsen burette) which allows for highly accurate measurements (the scale is read up to a precision of 0.005 mL). From 0 to 16 the burette isn't divided, that usually starts from 16 and goes until 20.5 or 21.5. A single double millimeter on a Knudsen burette scale corresponds to one permille of chloride in the seawater sample. This burette can be used for titration of water from all of the oceans and seas, with the exemptions being areas with very low salinity (e.g. the Baltic Sea) and river estuaries which require the use of normal burettes.

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Knudsen’s pipette    →   Knudsenova pipeta

Kudsen's automatic pipette, developed by the Danish physicist Martin Knudsen (1871-1949), allows quick and accurate transfer of a constant volume of liquid (sea water), usually around 15 mL. On the top of pipette is a double sided C vent that can establish flow between the body of the pipette and one of the branches (A or B), or isolate the body of the pipette from both of the branches. Sucking through the B branch the pipette is filled with liquid, it is closed with a twist of the C valve and the liquid is released by rotating the valve towards the A branch (so atmospheric air can enter the pipette). Emptying the pipette takes around 30 seconds. Before it's first use, the pipette must be calibrated with distilled water.

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