Standard conditions for temperature and pressure

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In chemistry, standard condition for temperature and pressure (informally abbreviated as STP) 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 (IUPAC) and the National Institute of Standards and Technology (NIST), although these are not universally accepted 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 °C (273.15 K, 32 °F) and an absolute pressure of 100 kPa (14.504 psi, 0.986 atm),[1] while NIST's version is a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 101.325 kPa (14.696 psi, 1 atm). International Standard Metric Conditions for natural gas and similar fluids [2] is 288.15 Kelvin and 101.325 kPa.

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 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. Good practice is to incorporate the reference conditons wherever ambiguity is possible i.e. V(273.15K, 101.325kPa)m3.



Past use

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 K; 32.00 °F) and 101.325 kPa (1 atm or 760 Torr). During those same years, the most commonly used standard reference conditions for people using the imperial or U.S. customary systems was 60 °F (15.56 °C; 288.71 K) and 14.696 psi (1 atm) because it was almost universally used by the oil and gas industries worldwide. However, the above two definitions are no longer the most commonly used in either system of units.

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