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| {{distinguish|Standard state}}
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| '''Standard conditions for temperature and pressure''' are [[Technical standard|standard]] sets of conditions for experimental measurements established 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.
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| In chemistry, IUPAC established '''standard temperature and pressure''' (informally abbreviated as '''STP''') as a [[temperature]] of 273.15 [[Kelvin|K]] (0 °C, 32 °F) and an [[absolute pressure]] of 100 [[Pascal (unit)|kPa]] (14.504 [[pound-force per square inch|psi]], 0.987 [[Atmosphere_(unit)|atm]], [[Bar_(unit)|1 bar]]).<ref name="IUPAC">{{cite book|title=IUPAC. Compendium of Chemical Terminology|year=1997|publisher=Blackwell Scientific Publications|location=Oxford|isbn=0-9678550-9-8|url=http://goldbook.iupac.org/PDF/S06036.pdf|author=A. D. McNaught and A. Wilkinson|edition=2nd|quote=Standard conditions for gases: Temperature, 273.15 K [...] and pressure of 10<sup>5</sup> pascals. The previous standard [[absolute pressure]] of 1 atm (equivalent to {{nowrap|1.01325 × 10<sup>5</sup> Pa}}) was changed to 100 [[Pascal (unit)|kPa]] in 1982. IUPAC recommends that the former pressure should be discontinued.}}</ref> An unofficial, but commonly used standard is '''standard [[ambient temperature]] and pressure''' ('''SATP''') as a [[temperature]] of 298.15 [[Kelvin|K]] (25 °C, 77 °F) and an [[absolute pressure]] of 100 [[Pascal (unit)|kPa]] (14.504 [[pound-force per square inch|psi]], 0.987 atm). The '''STP''' and the '''SATP''' should not be confused with the [[standard state]] commonly used in thermodynamic evaluations of the [[Gibbs free energy|Gibbs energy]] of a reaction.
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| [[National Institute of Standards and Technology|NIST]] uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 101.325 kPa (14.696 psi, 1 atm). The International Standard Metric Conditions for natural gas and similar fluids are {{convert|288.15|K|F C}} and 101.325 kPa.<ref name=ISO13443 />
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| 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 always incorporate the reference conditions of temperature and pressure.
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| ==Definitions==
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| ===Past use===
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| 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 {{convert|15|C|K F|2}} and {{convert|101.325|kPa|atm Torr|lk=on|abbr=on|sigfig=3}}. During those same years, the most commonly used standard reference conditions for people using the [[Imperial units|imperial]] or [[United States customary units|U.S. customary]] systems was {{convert|60|F|C K|2}} and 14.696 [[pound-force per square inch|psi]] (1 atm) because it was almost universally used by the oil and gas industries worldwide. The above definitions are no longer the most commonly used in either system of units.
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| ===Current use===
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| Many different definitions of standard reference 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. 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).<ref name="IUPAC 2">{{cite book |author= A. D. McNaught, A. Wilkinson |title=Compendium of Chemical Terminology, The Gold Book |url=http://www.iupac.org/goldbook/S05921.pdf |edition=2nd |year=1997 |publisher=Blackwell Science |isbn=0-86542-684-8 |quote=Standard pressure: Chosen value of pressure denoted by p<sup><s>o</s></sup> or p°. In 1982 IUPAC recommended the value 10<sup>5</sup> Pa, but prior to 1982 the value 101 325 Pa (= 1 atm) was usually used.}}</ref>
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| Natural gas companies in Europe and South America have adopted 15 °C (59 °F) and 101.325 kPa (14.696 psi) as their standard gas volume reference conditions.<ref>{{cite web |url=http://www.gassco.no/sw3138.asp |title= Concepts – Standard cubic meter (scm) |accessdate=2008-07-25 |author=[[Gassco]] |quote= Scm: The usual abbreviation for standard cubic metre – a cubic metre of gas under a standard condition, defined as an atmospheric pressure of 1.01325 [[bar (unit)|bar]] and a temperature of 15°C. This unit provides a measure for gas volume.}} {{Dead link|date=September 2010|bot=H3llBot}}</ref><ref>{{cite web |url=http://www.nord-stream.com/uploads/media/Nord_Stream_Route_Status_ENGLISH.pdf |title=Status of the Nord Stream pipeline route in the Baltic Sea |accessdate=2008-07-25 |author=[[Nord Stream]] |date=October 2007 |quote=bcm: Billion Cubic Meter (standard cubic metre – a cubic metre of gas under a standard condition, defined as an atmospheric pressure of 1 atm and a temperature of 15 °C.)}}</ref><ref>{{cite web |url=http://www.secinfo.com/dsD7y.1a.7.htm |title=Natural gas purchase and sale agreement |accessdate=2008-07-25 |author=[[Metrogas]] |date=June 2004 |quote=Natural gas at standard condition shall mean the quantity of natural gas, which at a temperature of fifteen (15) Celsius degrees and a pressure of 101.325 kilopascals occupies the volume of one (1) cubic meter.}}</ref> Also, the [[International Organization for Standardization]] (ISO), the [[United States Environmental Protection Agency]] (EPA) and [[National Institute of Standards and Technology]] (NIST) each have more than one definition of standard reference conditions in their various standards and regulations.
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| In Russia, State Standard GOST 2939-63 sets the following standard conditions: 20 °C (293.15 K), 760 mmHg (101325 N/m<sup>2</sup>) and zero humidity.
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| <center>
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| {| class="wikitable"
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| |+ '''Standard reference conditions in current use'''
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| ! Temperature !! Absolute pressure !! Relative humidity
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| !rowspan="2"| Publishing or establishing entity
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| !°C!!kPa!!% RH
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| |align="center"|0||align="center"|100.000|| ||International Union of Pure and Applied Chemistry|[[IUPAC]] (STP)<ref name=IUPAC/>
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| |align="center"|0||align="center"|101.325|| ||[[National Institute of Standards and Technology|NIST]],<ref name=NISTDataBase7>{{cite web |url=http://www.nist.gov/pml/data/star/index.cfm |title=NIST Standard Reference Database 124 – Stopping-Power and Range Tables for Electrons, Protons, and Helium Ions|accessdate=08-07-25 |author=[[National Institute of Standards and Technology|NIST]] |year=1989 |quote=If you want the program to treat the material as an ideal gas, the density will be assumed given by M/V, where M is the gram molecular weight of the gas and V is the mol volume of 22414 cm<sup>3</sup> at standard conditions (0 deg C and 1 atm).}}{{dead link|date=September 2013}}</ref> ISO 10780,<ref name=ISO10780>{{Cite web |author=[[International Organization for Standardization|ISO]] | title=ISO 10780:1994 : Stationary source emissions – Measurement of velocity and volume flowrate of gas streams in ducts |year=1994 |url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=18855}}</ref> formerly [[IUPAC]]<ref name=IUPAC/>
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| |align="center"|15||align="center"|101.325||align="center"|0<ref name=Handbook>{{cite book|author=Robert C. Weast (Editor)|title=Handbook of Physics and Chemistry|edition=56th|publisher=CRC Press|pages=F201–F206|year=1975|isbn=0-87819-455-X}}</ref><ref name=ISO13443>{{cite book |title=Natural gas – Standard reference conditions (ISO 13443) |publisher=International Organization for Standardization |location=Geneva, Switzerland |url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=20461 |year=1996}}</ref>||[[ICAO]]'s [[International Standard Atmosphere|ISA]],<ref name=Handbook/> ISO 13443,<ref name=ISO13443/> [[European Environment Agency|EEA]],<ref name=EEA>{{cite book |title=Extraction, First Treatment and Loading of Liquid & Gaseous Fossil Fuels (Emission Inventory Guidebook B521, Activities 050201 – 050303) |date=September 1999 |publisher=European Environmental Agency |location=Copenhagen, Denmark |url=http://reports.eea.eu.int/EMEPCORINAIR3/en/B521vs3.1.pdf |format=PDF}}</ref> EGIA<ref name=EGIA>"Electricity and Gas Inspection Act", SOR/86-131 (defines a set of standard conditions for Imperial units and a different set for metric units) [http://laws.justice.gc.ca/en/E-4/SOR-86-131/95708.html Canadian Laws]</ref>
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| |align="center"|20||align="center"|101.325|| ||[[United States Environmental Protection Agency|EPA]],<ref name=NSPS>"Standards of Performance for New Sources", 40 CFR—Protection of the Environment, Chapter I, Part 60, Section 60.2, 1990 [http://a257.g.akamaitech.net/7/257/2422/08aug20051500/edocket.access.gpo.gov/cfr_2005/julqtr/pdf/40cfr60.2.pdf New Source Performance Standards]</ref> NIST<ref name=NISTJournal>{{cite journal |title=Design and Uncertainty for a PVTt Gas Flow Standard |journal=Journal of Research of the National Institute of Standards and Technology |volume=108 |year=2003 |url=http://www.cstl.nist.gov/div836/836.01/PDFs/2003/j80wri.pdf |format=PDF |issue=1}}</ref>
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| |align="center"|25||align="center"|101.325|| ||EPA<ref name=NAAQS>"National Primary and Secondary Ambient Air Quality Standards", 40 CFR—Protection of the Environment, Chapter I, Part 50, Section 50.3, 1998 [http://a257.g.akamaitech.net/7/257/2422/08aug20051500/edocket.access.gpo.gov/cfr_2005/julqtr/pdf/40cfr50.3.pdf National Ambient Air Standards]</ref>
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| |align="center"|25||align="center"|100.000|| ||SATP<ref name=NBS>{{cite journal |title=Table of Chemical Thermodynamic Properties |author=National Bureau of Standards (NBS) |journal=Journal of Physics and Chemical Reference Data |year=1982 |volume=11 |issue=Supplement 2}}</ref>
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| |align="center"|20||align="center"|100.000||align="center"|0||[[Compressed Air and Gas Institute|CAGI]]<ref name=CAGI>{{cite web |title=Glossary |year=2002 |publisher=Compressed Air and Gas Institute |location=Cleveland, OH, USA |url=http://www.cagi.org/toolbox/glossary.htm}}</ref>
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| |align="center"|15||align="center"|100.000|| ||[[Society of Petroleum Engineers|SPE]]<ref name=SPE>{{cite web |url=http://www.spe.org/spe-site/spe/spe/papers/authors/Metric_Standard.pdf |format=PDF |title=The SI Metric System of Units and SPE Metric Standard |at=Notes for Table 2.3, on PDF page 25 of 42 PDF pages, define two different sets of reference conditions, one for the standard cubic foot and one for the standard cubic meter |publisher=Society of Petroleum Engineers}}</ref>
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| |align="center"|20||align="center"|101.3||align="center"|50|| ISO 5011<ref name=ISO5011>{{cite book |title=Air Intake Filters (ISO 5011:2002) |year=2002 |publisher=International Organization for Standardization |location=Geneva, Switzerland |url=http://www.iso.org/iso/en/prods-services/ISOstore/store.html}}</ref>
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| !°F!!psi!! % RH
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| |align="center"|60||align="center"|14.696|| ||SPE,<ref name=SPE/> U.S. [[Occupational Safety and Health Administration|OSHA]],<ref name=OSHA>"Storage and Handling of Liquefied Petroleum Gases" and "Storage and Handling of Anhydrous Ammonia", 29 CFR—Labor, Chapter XVII—Occupational Safety and Health Administration, Part 1910, Sect. 1910.110 and 1910.111, 1993 [http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=f169acd0f57a17565c9984fa0f57d285&rgn=div8&view=text&node=29:5.1.1.1.8.8.33.10&idno=29 Storage/Handling of LPG]</ref> [[SCAQMD]]<ref name=SCAQMD>"Rule 102, Definition of Terms (Standard Conditions)", Amended December 2004, South Coast Air Quality Management District, Los Angeles, California, USA [http://www.aqmd.gov/rules/reg/reg01/r102.pdf SCAQMD Rule 102]</ref>
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| |align="center"|60||align="center"|14.73|| ||EGIA,<ref name=EGIA/> [[Organization of Petroleum Exporting Countries|OPEC]],<ref name=OPEC>{{cite web |title=Annual Statistical Bulletin |year=2004 |editor=Omar Ibrahim |publisher=Organization of the Petroleum Exporting Countries |location=Vienna, Austria |url=http://www.opec.org/library/Annual%20Statistical%20Bulletin/pdf/ASB2004.pdf |format=PDF}}</ref> U.S. [[Energy Information Administration|EIA]]<ref name=EIA>{{cite web |title=Natural Gas Annual 2004 (DOE/EIA-0131(04)) |date=December 2005 |publisher=U.S. Department of Energy |author=Energy Information Administration |location=Washington, D.C., USA |url=http://tonto.eia.doe.gov/FTPROOT/natgas/013104.pdf |format=PDF}}</ref>
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| |align="center"|59||align="center"|14.503||align="center"|78|||U.S. Army Standard Metro<ref name=ArmyStdMetro>{{cite book|url=http://www.exteriorballistics.com/ebexplained/5th/31.cfm |title=Rifle and Handgun Reloading Manual |edition=5 |chapter= Chapter 3 – Effects of Altitude and Atmospheric Conditions (Exterior Ballistics Section) |author=Sierra Bullets L.P. |location=Sedalia, MO, USA-}}</ref>{{efn|The pressure is specified as 750 [[mmHg]]. However, the [[mmHg]] is temperature dependent, as mercury expands as temperature goes up. Here the values for the 0–20°C range are given.}}
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| |align="center"|59||align="center"|14.696||align="center"|60||ISO 2314,<ref name=ISO2314>{{cite book |title=Gas turbines – Acceptance tests (ISO 2314:1989) |year=1989 |edition=2 |publisher=International Organization for Standardization |location=Geneva, Switzerland |url=http://www.iso.org/iso/en/prods-services/ISOstore/store.html}}</ref> ISO 3977-2<ref name=ISO3977-2>{{cite book |title=Gas turbines – Procurement – Part 2: Standard reference conditions and ratings (ISO 3977-2:1997) |year=1997 |publisher=International Organization for Standardization |location=Geneva, Switzerland |url=http://www.iso.org/iso/en/prods-services/ISOstore/store.html}}</ref>
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| !°F!!in Hg!! % RH
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| |align="center"|70||align="center"|29.92||align="center"|0||[[Air Movement and Control Association|AMCA]],<ref name=AMCA>ANSI/AMCA Standard 210, "Laboratory Methods Of Testing Fans for Aerodynamic Performance Rating", as implied by [http://www.greenheck.com/pdf/centrifugal/Plug.pdf http://www.greenheck.com/pdf/centrifugal/Plug.pdf] when accessed on October 17, 2007</ref>{{efn|The standard is given as 29.92 [[inHg]] at an unspecified temperature. This most likely corresponds to a standard pressure of 101.325 kPa, converted into ~29.921 inHg at {{convert|32|F|C}}.}} air density = 0.075 lbm/ft³. This AMCA standard applies only to air.
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| |align="center"|59||align="center"|29.92|| ||[[Federal Aviation Administration]] (FAA)<ref name=FAA>{{cite book |url=http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2003.pdf |format=PDF |chapter=Chapter 3, Principles of Flight |title=Pilot's Handbook of Aeronautical Knowledge |publisher=Federal Aviation Administration}}</ref>
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| |}
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| </center>
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| Notes:
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| * EGIA: Electricity and Gas Inspection Act (of Canada)
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| * SATP: Standard Ambient Temperature and Pressure
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| ==International Standard Atmosphere==
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| In [[aeronautics]] and [[fluid dynamics]] the "[[International Standard Atmosphere]]" (ISA) is a specification of pressure, temperature, density, and speed of sound at each altitude. The International Standard Atmosphere is representative of atmospheric conditions at mid latitudes. In the USA this information is specified the [[U.S. Standard Atmosphere]] which is identical to the "International Standard Atmosphere" at all altitudes up to 65,000 feet above sea level.{{citation needed|date=May 2012}}
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| ==Standard laboratory conditions==
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| Due to the fact that many definitions of standard temperature and pressure differ in temperature significantly from standard laboratory temperatures (e.g., 0 °C vs. ~25 °C), reference is often made to "standard laboratory conditions" (a term deliberately chosen to be different from the term "standard conditions for temperature and pressure", despite its semantic near identity when interpreted literally). However, what is a "standard" [[laboratory]] temperature and pressure is inevitably culture-bound, given that different parts of the world differ in climate, altitude and the degree of use of heat/cooling in the workplace. For example, schools in [[New South Wales]], [[Australia]] use 25 °C at 100 kPa for standard laboratory conditions.<ref>{{cite book|author=Peter Gribbon|title=Excel HSC Chemistry Pocket Book Years 11–12|publisher=Pascal Press|year=2001|isbn=1-74020-303-8}}</ref>
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| [[ASTM International]] has published [[Technical standard|Standard]] ASTM E41- Terminology Relating to Conditioning and hundreds of special conditions for particular materials and [[test method]]s. Other [[standards organization]]s also have specialized standard test conditions.
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| ==Molar volume of a gas==
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| It is equally as important to indicate the applicable reference conditions of temperature and pressure when stating the molar volume of a gas<ref>{{cite web |url=http://physics.nist.gov/cgi-bin/cuu/Results?search_for=volume+molar |title=Fundamental Physical Properties: Molar Volumes (CODATA values for ideal gases) |publisher=[[National Institute of Standards and Technology|NIST]]}}</ref> as it is when expressing a gas volume or volumetric flow rate. Stating the molar volume of a gas without indicating the reference conditions of temperature and pressure has no meaning and it can cause confusion.
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| The molar gas volumes can be calculated with an accuracy that is usually sufficient by using the [[universal gas law]] for ideal gases. The usual expression is:
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| :<math>P V = nRT</math>
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| ...which can be rearranged thus:
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| :<math>\frac{V}{n} = \frac{RT}{P}</math>
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| where (in SI metric units):
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| {| border="0" cellpadding="2"
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| !align=right| ''P''
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| |align=left|= the absolute pressure of the gas, in [[pascal (unit)|Pa (pascal)]]
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| !align=right|''n''
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| |align=left|= [[amount of substance]], in [[mole (unit)|mol]]
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| !align=right| ''V''
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| |align=left|= the volume of the gas, in m<sup>3</sup>
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| !align=right| ''T''
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| |align=left|= the absolute temperature of the gas, in [[kelvin|K]]
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| !align=right| ''R''
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| |align=left|= the [[gas constant|universal gas law constant]] of 8.3145 m<sup>3</sup>·Pa/(mol·K)
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| |}
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| The molar volume of any ideal gas may be calculated at various standard reference conditions as shown below:
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| * '''V'''/'''n''' = 8.3145 × 273.15 / 101.325 = 22.414 m<sup>3</sup>/kmol at 0 °C and 101.325 kPa
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| * '''V'''/'''n''' = 8.3145 × 273.15 / 100.000 = 22.711 m<sup>3</sup>/kmol at 0 °C and 100 kPa
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| * '''V'''/'''n''' = 8.3145 × 298.15 / 101.325 = 24.466 m<sup>3</sup>/kmol at 25 °C and 101.325 kPa
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| * '''V'''/'''n''' = 8.3145 × 298.15 / 100.000 = 24.790 m<sup>3</sup>/kmol at 25 °C and 100 kPa
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| * '''V'''/'''n''' = 10.7316 × 519.67 / 14.696 = 379.48 ft<sup>3</sup>/lbmol at 60 °F and 14.696 psi (or about 0.8366 ft<sup>3</sup>/gram mole)
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| * '''V'''/'''n''' = 10.7316 × 519.67 / 14.730 = 378.61 ft<sup>3</sup>/lbmol at 60 °F and 14.73 psi
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| The technical literature can be confusing because many authors fail to explain whether they are using the universal gas law constant '''''R''''', which applies to any ideal gas, or whether they are using the gas law constant '''''R<sub>s</sub>''''', which only applies to a specific individual gas. The relationship between the two constants is '''''R<sub>s</sub>''''' = '''''R / M''''', where '''''M''''' is the molecular weight of the gas.
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| The [[US Standard Atmosphere]] (USSA) uses 8.31432 m<sup>3</sup>·Pa/(mol·K) as the value of ''R'' (see [[Gas constant]]) for all calculations. However, the USSA,1976 does recognize that this value is not consistent with the values of the Avogadro constant and the Boltzmann constant.<ref name="USSA1976">[http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539_1977009539.pdf U.S. Standard Atmosphere], 1976, U.S. Government Printing Office, Washington, D.C., 1976.</ref>
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| ==See also==
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| * [[Atmospheric models]]
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| * [[Environmental chamber]]
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| * [[ISO 1]] – standard reference temperature for geometric product specifications
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| * [[Standard Dry Air]]
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| * [[Standard state]]
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| ==Notes==
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| {{notelist|35em}}
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| ==References==
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| {{reflist|2}}
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| ==External links==
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| * [http://goldbook.iupac.org/S05910.html "Standard conditions for gases"] from the [[IUPAC]] ''Gold Book''.
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| * [http://goldbook.iupac.org/S05921.html "Standard pressure"] from the [[IUPAC]] ''Gold Book''.
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| * [http://goldbook.iupac.org/S06036.html "STP"] from the [[IUPAC]] ''Gold Book''.
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| * [http://goldbook.iupac.org/S05925.html "Standard state"] from the [[IUPAC]] ''Gold Book''.
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| [[Category:Atmospheric thermodynamics]]
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| [[Category:Aerodynamics]]
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| [[Category:Chemical engineering]]
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| [[Category:Environmental engineering]]
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| [[Category:Gases]]
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| [[Category:Measurement]]
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| [[Category:Mechanical engineering]]
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| [[Category:Physical chemistry]]
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| [[Category:Standards]]
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| [[Category:Thermodynamics]]
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