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The torr is defined as 1 / 760 of one standard atmosphere, while the atmosphere is defined as 101325 pascals. Therefore, 1 Torr is equal to 101325 / 760 Pa. The decimal form of this fraction (133.322 368 421 052 631 578 947) is an infinitely long, periodically repeating decimal (repetend length: 18).
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0 °C (32 °F) and standard gravity (g n = 9.806 65 m/s 2). [2] It was used as a reference condition for physical and chemical properties, and the definition of the centigrade temperature scale set 100 °C as the boiling point of water at this pressure.
For example, IUPAC has, since 1982, defined standard reference conditions as being 0 °C and 100 kPa (1 bar), in contrast to its old standard of 0 °C and 101.325 kPa (1 atm). [2] The new value is the mean atmospheric pressure at an altitude of about 112 metres, which is closer to the worldwide median altitude of human habitation (194 m).
1 atm ≡ 101 325: ≡ 1.013 25: 1.0332 — 760 14.695 948 775 5142: 1 Torr 133.322 368 421: 0.001 333 224: 0.001 359 51
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth.The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, [1] 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. [2]
At the normal boiling point of a liquid, the vapor pressure is equal to the standard atmospheric pressure defined as 1 atmosphere, [1] 760 Torr, 101.325 kPa, or 14.69595 psi. For example, at any given temperature, methyl chloride has the highest vapor pressure of any of the liquids in the chart.
One millimetre of mercury is approximately 1 torr, which is 1 / 760 ... 1 atm ≡ 101 325: ≡ 1.013 25: 1.0332 — 760 14.695 948 775 5142: 1 Torr 133.322 368 ...
Unlike the mmHg, the torr (with its modern definition of 1/760 1 atm = 101325/760 Pa) is a perfectly legitimate unit of pressure, derived from SI units. Its use in general is discouraged, [3] since the SI unit of pressure is the pascal.