Standard temperature and pressure explained

Standard temperature and pressure (STP) or Standard conditions for temperature and pressure are various standard sets of conditions for experimental measurements used 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. Other organizations have established a variety of other definitions.

In industry and commerce, the standard conditions for temperature and pressure are often necessary for expressing 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 (Sm3/s), and normal cubic meters per second (Nm3/s).

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 special cases this can lead to confusion and errors. Good practice always incorporates the reference conditions of temperature and pressure. If not stated, some room environment conditions are supposed, close to 1 atm pressure, 293 K (20 °C), and 0% humidity.

Definitions

In chemistry, IUPAC changed its definition of standard temperature and pressure in 1982:[1] [2]

NIST uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa).[3] This standard is also called normal temperature and pressure (abbreviated as NTP). 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).[4] [5] NIST also uses 15 °C (59 °F) for the temperature compensation of refined petroleum products, despite noting that these two values are not exactly consistent with each other.[6]

The ISO 13443 standard reference conditions for natural gas and similar fluids are 288.15K and 101.325 kPa;by contrast, the American Petroleum Institute adopts 60F.[7]

Past uses

Before 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 15C and 101.325kPa. During those same years, the most commonly used standard reference conditions for people using the imperial or U.S. customary systems was 60F and 14.696 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.[8]

Current use

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). 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).[9]

Natural gas companies in Europe, Australia, and South America have adopted 15 °C (59 °F) and 101.325 kPa (14.696 psi) as their standard gas volume reference conditions, used as the base values for defining the standard cubic meter.[10] [11] [12] 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.

Temperature! colspan=4
PressureHumidityPublishing or establishing entity
°C°FkPammHgpsiinHg%
 
0disp=tablecenNaNdisp=tablecen100disp=tablecenNaNdisp=tablecenInternational Union of Pure and Applied ChemistryIUPAC (STP) since 1982
0disp=tablecenNaNdisp=tablecen101.325disp=tablecenNaNdisp=tablecenNIST,[13] ISO 10780,[14] formerly IUPAC (STP) until 1982
15disp=tablecenNaNdisp=tablecen101.325disp=tablecenNaNdisp=tablecen0 ICAO's ISA,[15] ISO 13443,[16] EEA,[17] EGIA (SI Definition)[18] Density 1.225 kg/m³
20disp=tablecenNaNdisp=tablecen101.325disp=tablecenNaNdisp=tablecenEPA,[19] NIST.[20] [21] [22]
22C101.325disp=tablecenNaNdisp=tablecenAmerican Association of Physicists in Medicine[23]
25disp=tablecenNaNdisp=tablecen101.325disp=tablecenNaNdisp=tablecen SATP,[24] EPA[25]
20disp=tablecenNaNdisp=tablecen100disp=tablecenNaNdisp=tablecen0CAGI[26]
15disp=tablecenNaNdisp=tablecen100disp=tablecenNaNdisp=tablecen SPE[27]
20disp=tablecenNaNdisp=tablecen101.3disp=tablecenNaNdisp=tablecen50ISO 5011[28]
20disp=tablecenNaNdisp=tablecen760mmHg760disp=numberNaNdisp=number760disp=numberNaNdisp=number0GOST 2939-63
60F14.696psi14.696disp=numberNaNdisp=numberSPE, U.S. OSHA,[29] SCAQMD[30]
60F14.73psi14.73disp=numberNaNdisp=numberEGIA (Imperial System Definition)
60F14.7psi14.7psi U.S. DOT (SCF)[31]
59F14.503psi14.503disp=numberNaNdisp=number78U.S. Army Standard Metro[32]
59F14.696psi14.696disp=numberNaNdisp=number60ISO 2314,[33] ISO 3977-2,[34] ASHRAE Fundamentals Handbook[35]
70F29.92inHg0AMCA,[36] air density = 0.075 lbm/ft3.[37] [38]
59F29.92inHgFAA[39]
20disp=tablecenNaNdisp=tablecen101.325disp=tablecenNaNdisp=tablecen0 EN 14511-1:2013[40]
15disp=tablecenNaNdisp=tablecen101.325disp=tablecenNaNdisp=tablecen0ISO 2533:1975[41] ISO 13443:2005,[42] ISO 7504:2015[43]
0disp=tablecenNaNdisp=tablecen101.325disp=tablecenNaNdisp=tablecen0DIN 1343:1990[44]

Abbreviations:

International Standard Atmosphere

In aeronautics and fluid dynamics the "International Standard Atmosphere" (ISA) is a specification of pressure, temperature, density, and speed of sound at each altitude. At standard mean sea level it specifies a temperature of 15C, pressure of 101325Pa (1 atm), and a density of 1.225kg/m3. It also specifies a temperature lapse rate of −6.5 °C (-11.7 °F) per km (approximately −2 °C (-3.6 °F) per 1,000 ft).[45] [46]

The International Standard Atmosphere is representative of atmospheric conditions at mid latitudes. In the US 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.

Standard laboratory conditions

Because 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 geography-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.[47] ASTM International has published Standard ASTM E41- Terminology Relating to Conditioning and hundreds of special conditions for particular materials and test methods. Other standards organizations also have specialized standard test conditions.

Molar volume of a gas

See also: Standard cubic feet.

It is as important to indicate the applicable reference conditions of temperature and pressure when stating the molar volume of a gas[48] 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 very little meaning and can cause confusion.

The molar volume of gases around STP and at atmospheric pressure can be calculated with an accuracy that is usually sufficient by using the ideal gas law. The molar volume of any ideal gas may be calculated at various standard reference conditions as shown below:

Technical literature can be confusing because many authors fail to explain whether they are using the ideal gas constant R, or the specific gas constant Rs. The relationship between the two constants is Rs = R / m, where m is the molecular mass of the gas.

The US Standard Atmosphere (USSA) uses 8.31432 m3·Pa/(mol·K) as the value of R. However, the USSA in 1976 does recognize that this value is not consistent with the values of the Avogadro constant and the Boltzmann constant.[49]

See also

External links

Notes and References

  1. Book: IUPAC. Compendium of Chemical Terminology. 1997. Blackwell Scientific Publications. Oxford. 0-632-03583-8. A. D. McNaught and A. Wilkinson. Alan. McNaught. Aubrey. Jenkins. Bedřich. Košata. Jiří. Jirát. Miloslav. Nič. 2nd. 54. 10.1351/goldbook. Standard conditions for gases: ... and pressure of 105 pascals. The previous standard absolute pressure of 1 atm (equivalent to 101.325 kPa) was changed to 100 kPa in 1982. IUPAC recommends that the former pressure should be discontinued..
  2. Book: standard pressure. IUPAC. Compendium of Chemical Terminology. 1997. Blackwell Scientific Publications. Oxford. 978-0-9678550-9-7. https://goldbook.iupac.org/terms/view/S05921. A. D. McNaught and A. Wilkinson. 2nd. 10.1351/goldbook.S05921.
  3. 20 Degrees Celsius--A Short History of the Standard Reference Temperature for Industrial Dimensional Measurements. NIST . January 2007 . 112 . 1 . 1–23 . Doiron . Theodore D. . 10.6028/jres.112.001 . 27110451 . 4654601 .
  4. Book: Helrich, Carl S.. Modern Thermodynamics with Statistical Mechanics. 2008-11-14. Springer Science & Business Media. 978-3-540-85418-0. en.
  5. Web site: A Guide to the NIST Chemistry WebBook. 2020-10-06. webbook.nist.gov.
  6. Web site: Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. 3-1.
  7. https://www.api.org/-/media/files/publications/2022-catalog/petroleum-measurement-2022.pdf API Petroleum Measurement
  8. 20 °C – A Short History of the Standard Reference Temperature for Industrial Dimensional Measurements. Doiron. Ted. Jan–Feb 2007. Journal of Research of the National Institute of Standards and Technology. 112. 1. 1–23. 10.6028/jres.112.001. 27110451. 4654601.
  9. Hypsographic demography: The distribution of human population by altitude. Cohen. Joel E.. Small. Christopher. November 24, 1998. Proceedings of the National Academy of Sciences. 95. 24. 14009–14014. 10.1073/pnas.95.24.14009. 9826643. 24316. 1998PNAS...9514009C . free.
  10. Web site: Concepts – Standard cubic meter (scm) . 2008-07-25 . Gassco . 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 and a temperature of 15°C. This unit provides a measure for gas volume. . dead . https://web.archive.org/web/20071018212002/http://www.gassco.no/sw3138.asp . October 18, 2007 . Gassco .
  11. Web site: Status of the Nord Stream pipeline route in the Baltic Sea . https://web.archive.org/web/20080216043432/http://www.nord-stream.com/uploads/media/Nord_Stream_Route_Status_ENGLISH.pdf . dead . 2008-02-16 . 2008-07-25 . Nord Stream . October 2007 . 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.). Nord Stream .
  12. Web site: Natural gas purchase and sale agreement . 2008-07-25 . Metrogas . June 2004 . 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.. Metrogas .
  13. Web site: NIST Standard Reference Database 124 – Stopping-Power and Range Tables for Electrons, Protons, and Helium Ions . 2008-07-25 . NIST . 1989 . 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 cm3 at standard conditions (0 deg C and 1 atm). . dead . https://web.archive.org/web/20101006154629/https://www.nist.gov/pml/data/star/index.cfm . October 6, 2010 . National Institute of Standards and Technology .
  14. Web site: ISO . ISO 10780:1994 : Stationary source emissions – Measurement of velocity and volume flowrate of gas streams in ducts . 1994 . International Organization for Standardization .
  15. Book: Robert C. Weast . Handbook of Physics and Chemistry. 56th. CRC Press. F201–F206. 1975. 978-0-87819-455-1.
  16. Book: Natural gas – Standard reference conditions (ISO 13443) . International Organization for Standardization . Geneva, Switzerland . 1996.
  17. Book: Extraction, First Treatment and Loading of Liquid & Gaseous Fossil Fuels (Emission Inventory Guidebook B521, Activities 050201 – 050303) . September 1999 . European Environmental Agency . Copenhagen, Denmark . PDF .
  18. "Electricity and Gas Inspection Act", SOR/86-131 (defines a set of standard conditions for Imperial units and a different set for metric units)  Canadian Laws.
  19. "Standards of Performance for New Sources", 40 CFR—Protection of the Environment, Chapter I, Part 60, Section 60.2, 1990.
  20. Design and Uncertainty for a PVTt Gas Flow Standard . Journal of Research of the National Institute of Standards and Technology . 108 . 2003 . https://web.archive.org/web/20040721040809/http://www.cstl.nist.gov/div836/836.01/PDFs/2003/j80wri.pdf . dead . 2004-07-21 . 1 . 21–47 . 10.6028/jres.108.004 . 27413592 . 4844527 . Wright . J. D. . Johnson . A. N. . Moldover . M. R. .
  21. (Also called NTP, Normal Temperature and Pressure.)
  22. Web site: What is the difference between STP and NTP?. Socratic . 2018-08-28 . https://web.archive.org/web/20151127035351/http://socratic.org/questions/what-is-the-difference-between-stp-and-ntp . 2015-11-27 . dead .
  23. AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams. Medical Physics . 26 . 1999. 9. 1847–1870 . 10.1118/1.598691. 10505874 . 1999MedPh..26.1847A. Almond . Peter R. . Biggs . Peter J. . Coursey . B. M. . Hanson . W. F. . Huq . M. Saiful . Nath . Ravinder . Rogers . D. W. O. . 12687636 . free .
  24. "CRC Handbook of Chemistry and Physics", Definition of Ambient, Chapter 1-26, 95th Edition, William M. Haynes, ed., CRC Press, Boca Raton, FL, 2014.
  25. "National Primary and Secondary Ambient Air Quality Standards", 40 CFR—Protection of the Environment, Chapter I, Part 50, Section 50.3, 1998.
  26. Web site: Glossary . 2002 . Compressed Air and Gas Institute . Cleveland, OH, US . https://web.archive.org/web/20070902020158/http://www.cagi.org/toolbox/glossary.htm . dead . 2007-09-02.
  27. Web site: The SI Metric System of Units and SPE Metric Standard (1982) . Standard Temperature (Page 24), and 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 . Society of Petroleum Engineers.
  28. Book: Air Intake Filters (ISO 5011:2002) . 2002 . International Organization for Standardization . Geneva, Switzerland .
  29. "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  Storage/Handling of LPG.
  30. "Rule 102, Definition of Terms (Standard Conditions)", Amended December 2004, South Coast Air Quality Management District, Los Angeles, California, US  SCAQMD Rule 102
  31. Web site: 49 C.F.R. § 171 . 22 May 2018.
  32. Book: http://www.exteriorballistics.com/ebexplained/5th/31.cfm . Rifle and Handgun Reloading Manual . 5 . Chapter 3 – Effects of Altitude and Atmospheric Conditions (Exterior Ballistics Section) . Sierra Bullets . Sedalia, MO, US . 2006-02-03 . 2006-03-09 . https://web.archive.org/web/20060309023230/http://www.exteriorballistics.com/ebexplained/5th/31.cfm . dead .
  33. Book: Gas turbines – Acceptance tests (ISO 2314:2009) . 2009 . 2 . International Organization for Standardization . Geneva, Switzerland .
  34. Book: Gas turbines – Procurement – Part 2: Standard reference conditions and ratings (ISO 3977-2:1997) . 1997 . International Organization for Standardization . Geneva, Switzerland .
  35. Web site: ASHRAE Handbook Online . 2023-08-09 . www.ashrae.org.
  36. ANSI/AMCA Standard 210, "Laboratory Methods Of Testing Fans for Aerodynamic Performance Rating", as implied by http://www.greenheck.com/pdf/centrifugal/Plug.pdf when accessed on October 17, 2007.
  37. This AMCA standard applies only to air; Compressed Gas Association [CGA] applies to industrial gas use in US.
  38. Book: Compressed Gas Handbook. 22 Nov 2017. 9781461306733. Association. Compressed Gas. 2012-12-06. Springer .
  39. Book: 2016. Pilot's Handbook of Aeronautical Knowledge. U.S. Department of Transportation Federal Aviation Administration. 43.
  40. Book: Air Conditioners, liquid chilling packages and heat pumps with electrically driven compressors for space heating and cooling . 2013 . BSI EN. UK.
  41. Book: Standard Atmosphere. 1975. International Organization for Standardization. Geneva, Switzerland.
  42. Book: Natural gas - Standard reference conditions. 1996. International Organization for Standardization. Geneva, Switzerland.
  43. Book: Gas analysis - Vocabulary. 2015. International Organization for Standardization. Geneva, Switzerland.
  44. Book: Referenzzustand, Normzustand, Normvolumen; Begriffe und Werte. 1990. Deutsches Institut für Normung. Germany.
  45. Web site: Auld . D.J. . Srinivas . K. . Properties of the Atmosphere . 2008 . 2008-03-13 . https://web.archive.org/web/20130609091708/http://www.aeromech.usyd.edu.au/aero/atmosphere/ . 2013-06-09 . dead .
  46. Batchelor, G. K., An Introduction to Fluid Dynamics, Cambridge Univ. Press, 1967.
  47. Book: Peter Gribbon. Excel HSC Chemistry Pocket Book Years 11–12. Pascal Press. 2001. 978-1-74020-303-6.
  48. Web site: Fundamental Physical Properties: Molar Volumes (CODATA values for ideal gases) . NIST.
  49. https://www.ngdc.noaa.gov/stp/space-weather/online-publications/miscellaneous/us-standard-atmosphere-1976/us-standard-atmosphere_st76-1562_noaa.pdf U.S. Standard Atmosphere, 1976

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Standard temperature and pressure".

Except where otherwise indicated, Everything.Explained.Today is © Copyright 2009-2024, A B Cryer, All Rights Reserved. Cookie policy.