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). For example, IUPAC has, since 1982, defined standard reference conditions as being 0 ☌ and 100 kPa (1 bar), in contrast to its old standard of 0 ☌ and 101.325 kPa (1 atm). Some of these organizations used other standards in the past. The table below lists a few of them, but there are more. Many different definitions of standard reference conditions are currently being used by organizations all over the world. The above definitions are no longer the most commonly used in either system of units. customary systems was 60 ☏ (15.56 ☌ 288.71 K) and 14.696 psi (1 atm) because it was almost universally used by the oil and gas industries worldwide. During those same years, the most commonly used standard reference conditions for people using the imperial or U.S. Past uses īefore 1918, many professionals and scientists using the metric system of units defined the standard reference conditions of temperature and pressure for expressing gas volumes as being 15 ☌ (288.15 K 59.00 ☏) and 101.325 kPa (1.00 atm 760 Torr). The ISO 13443 standard reference conditions for natural gas and similar fluids are 288.15 K (15.00 ☌ 59.00 ☏) and 101.325 kPa īy contrast, the American Petroleum Institute adopts 60 ☏ (15.56 ☌ 288.71 K). NIST also uses "15 ☌ (60 ☏)" for the temperature compensation of refined petroleum products, despite noting that these two values are not exactly consistent with each other. However, a common temperature and pressure in use by NIST for thermodynamic experiments is 298.15 K (25° C, 77° F) and 1 bar (14.5038 psi, 100 kPa). This standard is also called normal temperature and pressure (abbreviated as NTP). Since 1982, STP has been defined as a temperature of 273.15 K (0 ☌, 32 ☏) and an absolute pressure of exactly 10 5 Pa (100 kPa, 1 bar).Until 1982, STP was defined as a temperature of 273.15 K (0 ☌, 32 ☏) and an absolute pressure of exactly 1 atm (101.325 kPa).In chemistry, IUPAC changed its definition of standard temperature and pressure in 1982: If not stated, some room environment conditions are supposed, close to 1 atm pressure, 293 K (20 ☌), and 0% humidity. ![]() Good practice always incorporates the reference conditions of temperature and pressure. In special cases this can lead to confusion and errors. However, many technical publications (books, journals, advertisements for equipment and machinery) simply state "standard conditions" without specifying them often substituting the term with older "normal conditions", or "NC". In industry and commerce, the standard conditions for temperature and pressure are often necessary to define the standard reference conditions to express the volumes of gases and liquids and related quantities such as the rate of volumetric flow (the volumes of gases vary significantly with temperature and pressure): standard cubic meters per second (Sm 3/s), and normal cubic meters per second (Nm 3/s). Other organizations have established a variety of alternative definitions for their standard reference conditions. The most used standards are those of the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST), although these are not universally accepted standards. Standard temperature and pressure ( STP) are various standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. For the conditions used in thermodynamic evaluations, see Standard state.
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