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( Standard conditions)
In physical sciences, standard conditions for temperature and pressure are standard sets of conditions for experimental measurements, to allow comparisons to be made between different sets of data. The most used standards are those of the International Union of Pure and Applied Chemistry and the National Institute of Standards and Technology but are far from being universal standards. Other organizations have established a variety of alternative definitions for their standard reference conditions. The current version of IUPAC's standard is a temperature of 0&_160;°C (273.15&_160;K, 32&_160;°F) and an absolute pressure of 100&_160;kPa (14.504 psi)[1], while NIST's version is a temperature of 20&_160;°C (293.15&_160;K, 68&_160;°F) and an absolute pressure of 101.325&_160;kPa (14.696&_160;psi). In industry and commerce, 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 and liquids vary significantly with temperature and pressure). However many technical publications (books, journals, advertisements for equipment and machinery) simply state "standard conditions" without specifying them, often leading to confusion and errors. In the last five to six decades, professionals and scientists using the metric system of units defined the standard reference conditions of temperature and pressure for expressing gas volumes as being 0 °C (273.15&_160;K) and 101.325&_160;kPa (1&_160;atm).[citation needed] During those same years, the most commonly used standard reference conditions for people using the Imperial units or U.S. customary units was 60&_160;°F (520&_160;°R) and 14.696&_160;psi (1&_160;atm) because it was almost universally used by the oil and gas industries worldwide.[citation needed] However, the above two definitions are no longer the most commonly used in either system of units. Many different definitions of standard references conditions are currently being used by organizations all over the world. The table below lists a few of them, but there are more. Some of these organizations used other standards in the past, such as IUPAC which currently defines standard reference conditions as being 0&_160;°C and 100&_160;kPa (1&_160;bar) of pressure rather since 1982, in contrast to their old standard of 0&_160;°C and 101.325&_160;kPa (1&_160;atm).[2] Another example is from the oil industry. While a standard of 60&_160;°F and 14.696&_160;psi was used in the past, the current usage (particularly in North America) is predominantly of 60&_160;°F and 14.73&_160;psi.
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