CHEMISTRY GLOSSARY

critical pressure    →   kritični tlak

Critical pressure is the pressure of a fluid in its critical point; i.e. when it is at its critical temperature and critical volume.

critical volume    →   kritični volumen

Critical volume is the volume of a fixed mass of a fluid at critical temperature and pressure.

atmospheric pressure    →   atmosferski tlak

Atmospheric pressure is the pressure exerted by weight of the air above it at any point on the earth’s surface. At sea level the atmosphere will support a column of mercury about 760 mm high. This decreases with increasing altitude. The standard value for the atmospheric pressure at sea level in SI units is 101 325 Pa.

partial pressure    →   parcijalni tlak

Partial pressure is a pressure that one component of gas mixture would have if it were alone in the same volume and at the same temperature as the mixture is in now.

pressure    →   tlak

Pressure (p) is the force acting normally on unit area of a surface. It is measured in pascals in Si units (Pa)

vapour pressure    →   tlak pare

Vapour pressure is the pressure of a gas in equilibrium with a liquid (or, in some usage, a solid) at a specified temperature.

osmotic pressure    →   osmotski tlak

Osmotic pressure (Π) is the excess pressure necessary to maintain osmotic equilibrium between a solution and a pure solvent separated by a membrane permeable only to the solvent. In an ideal dilute solution

where c_B is the amount-of-substance concentration of the solute, R is the molar gas constant, and T the temperature.

critical point    →   kritična točka

In general, critical point is the point on the phase diagram of a two-phase system at which the two coexisting phases have identical properties and therefore represent a single phase. At the liquid-gas critical point of a pure substance, the distinction between liquid and gas vanishes, and the vapour pressure curve ends. The coordinates of this point are called the critical temperature and critical pressure. Above the critical temperature it is not possible to liquefy the substance.

critical temperature    →   kritična temperatura

Critical temperature is the temperature of the liquid-vapour critical point, that is, the temperature above which a gas cannot be liquefied by an increase of pressure.

critical mass    →   kritična masa

Critical mass is the minimum mass of a fissionable material (²³⁵U or ²³⁹Pu) that will initiate an uncontrolled chain reaction as in an atomic bomb. The critical mass of pure ²³⁹Pu is about 4.5 kg, and of ²³⁵U about 15 kg.