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Standard conditions for temperature and pressure
Standard conditions for temperature and pressure are 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.
In chemistry, IUPAC established standard temperature and pressure (informally abbreviated as STP) as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 100,000 Pa (1 bar, 14.5 psi, 0.9869 atm).<ref name="IUPAC">Template:Cite book</ref> An unofficial, but commonly used standard is standard ambient temperature and pressure (SATP) as a temperature of 298.15 K (25 °C, 77 °F). The STP and the SATP should not be confused with the standard state commonly used in thermodynamic evaluations of the Gibbs energy of a reaction.
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 Template:Convert and 101.325 kPa.<ref name=ISO13443 />
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.
Definitions
Past use
In the last five to six decades,Template:When professionals and scientists using the metric system of units defined the standard reference conditions of temperature and pressure for expressing gas volumes as being Template:Convert and Template:Convert. During those same years, the most commonly used standard reference conditions for people using the imperial or U.S. customary systems was Template:Convert 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.
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).<ref name="IUPAC 2">Template:Cite book</ref>
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>Template:Cite web Template:Dead link</ref><ref>Template:Cite web</ref><ref>Template:Cite web</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.
In Russia, State Standard GOST 2939-63 sets the following standard conditions: 20 °C (293.15 K), 760 mmHg (101325 N/m2) and zero humidity.
| Temperature | Absolute pressure | Relative humidity | Publishing or establishing entity |
|---|---|---|---|
| °C | kPa | % | |
| 0 | 100.000 | IUPAC (STP)<ref name=IUPAC/> | |
| 0 | 101.325 | NIST,<ref name=NISTDataBase7>Template:Cite webTemplate:Dead link</ref> ISO 10780,<ref name=ISO10780>Template:Cite web</ref> formerly IUPAC<ref name=IUPAC/> | |
| 15 | 101.325 | 0<ref name=ISO13443>Template:Cite book</ref><ref name=Handbook>Template:Cite book</ref> | ICAO's ISA,<ref name=Handbook/> ISO 13443,<ref name=ISO13443/> EEA,<ref name=EEA>Template:Cite book</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) Canadian Laws</ref> |
| 20 | 101.325 | EPA,<ref name=NSPS>"Standards of Performance for New Sources", 40 CFR—Protection of the Environment, Chapter I, Part 60, Section 60.2, 1990 New Source Performance Standards</ref> NIST<ref name=NISTJournal>Template:Cite journal</ref> | |
| 22 | 101.325 | 20-80 | American Association of Physicists in Medicine<ref name=MedPHys>Template:Cite journal</ref> |
| 25 | 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 National Ambient Air Standards</ref> | |
| 25 | 100.000 | SATP<ref name=NBS>Template:Cite journal</ref> | |
| 20 | 100.000 | 0 | CAGI<ref name=CAGI>Template:Cite web</ref> |
| 15 | 100.000 | SPE<ref name=SPE>Template:Cite web</ref> | |
| 20 | 101.3 | 50 | ISO 5011<ref name=ISO5011>Template:Cite book</ref> |
| °F | psi | % | |
| 60 | 14.696 | SPE,<ref name=SPE/> U.S. 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 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 SCAQMD Rule 102</ref> | |
| 60 | 14.73 | EGIA,<ref name=EGIA/> OPEC,<ref name=OPEC>Template:Cite web</ref> U.S. EIA<ref name=EIA>Template:Cite web</ref> | |
| 59 | 14.503 | 78 | U.S. Army Standard Metro<ref name=ArmyStdMetro>Template:Cite book</ref>Template:Efn |
| 59 | 14.696 | 60 | ISO 2314,<ref name=ISO2314>Template:Cite book</ref> ISO 3977-2<ref name=ISO3977-2>Template:Cite book</ref> |
| °F | inHg | % | |
| 70 | 29.92 | 0 | AMCA,<ref name=AMCA>ANSI/AMCA Standard 210, "Laboratory Methods Of Testing Fans for Aerodynamic Performance Rating", as implied by https://www.greenheck.com/pdf/centrifugal/Plug.pdf when accessed on October 17, 2007</ref>Template:Efn air density = 0.075 lbm/ft³. This AMCA standard applies only to air. |
| 59 | 29.92 | Federal Aviation Administration (FAA)<ref name=FAA>Template:Cite book</ref> |
Notes:
- EGIA: Electricity and Gas Inspection Act (of Canada)
- SATP: Standard Ambient Temperature and Pressure
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. 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.Template:Citation needed
Standard laboratory conditions
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>Template:Cite book</ref>
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
It is equally as important to indicate the applicable reference conditions of temperature and pressure when stating the molar volume of a gas<ref>Template:Cite web</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 very little meaning and can cause confusion.
The molar volume of gases around STP 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:
- Vm = 8.3145 × 273.15 / 101.325 = 22.414 dm3/mol at 0 °C and 101.325 kPa
- Vm = 8.3145 × 273.15 / 100.000 = 22.711 dm3/mol at 0 °C and 100 kPa
- Vm = 8.3145 × 298.15 / 101.325 = 24.466 dm3/mol at 25 °C and 101.325 kPa
- Vm = 8.3145 × 298.15 / 100.000 = 24.790 dm3/mol at 25 °C and 100 kPa
- Vm = 10.7316 × 519.67 / 14.696 = 379.48 ft3/lbmol at 60 °F and 14.696 psi (or about 0.8366 ft3/gram mole)
- Vm = 10.7316 × 519.67 / 14.730 = 378.61 ft3/lbmol at 60 °F and 14.73 psi
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 weight of the gas.
The US Standard Atmosphere (USSA) uses 8.31432 m3·Pa/(mol·K) as the value of R. 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">U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C., 1976.</ref>
See also
- Atmospheric models
- Environmental chamber
- ISO 1 – standard reference temperature for geometric product specifications
- Standard Dry Air
- Standard state
- standard sea level
Notes
References
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<references group=""></references>External links
- "Standard conditions for gases" from the IUPAC Gold Book.
- "Standard pressure" from the IUPAC Gold Book.
- "STP" from the IUPAC Gold Book.
- "Standard state" from the IUPAC Gold Book.
