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Standard conditions for temperature andpressure

From Wikipedia, the free encyclopedia

(Redirected from Standard temperature and pressure)

In chemistry and other sciences, STP or standard temperature and pressure is a standard set of

conditions for experimental measurements, to enable comparisons to be made between sets of data.

Internationally, the current STP defined by the IUPAC (International Union of Pure and Applied

Chemistry) is an absolute pressure of 100 kPa (1 bar) and a temperature of 273.15 K (0 °C).[1] Otherorganizations have established a variety of alternative definitions for the standard reference

conditions of temperature and pressure, such as the SATP amongst others.

In industry and commerce, it is necessary to define the standard reference conditions of temperature

and pressure when expressing a gas volume or a volumetric flow rate because the volume of a gas

varies with the temperature and pressure of the gas. The available data on the various definitions ofstandard reference conditions clearly indicates that the IUPAC's STP is not a universally accepted

definition of the standard conditions of temperature and pressure. For that reason, simply stating that

a gas flow rate is 10,000 m³/h (i.e. cubic meters per hour) at "standard conditions" or at "STP" has no

meaning unless the reference conditions that were applied are clearly stated.

In aeronautics and fluid dynamics the term "International Standard Atmosphere" is often used to

denote the variation of the principal thermodynamic variables (pressure, temperature, density, etc.)

of the atmosphere with altitude at mid latitudes.

Definitions used in the past

For a great many years, most engineers, chemists, physicists and other 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) and 101.325 kPa (i.e., 1 atmosphere of absolute pressure).

During those same years, the most commonly used standard reference conditions for people using

the Imperial or customary USA system of units was 60 °F (520 °R) and 14.696 psia (i.e., 1

atmosphere of absolute pressure) because it was almost universally used by the oil and gas industries

worldwide.

The above two definitions are no longer the most commonly used definitions in either the metric,

Imperial or the customary USA system of units. Some of the many different definitions currently in

use are presented in the next section.

It was also common in the past, when using the metric system of units, to refer to a Normal Cubic

Meter (Nm³) and to define it as being at 0 °C (273.15 K) and 101.325 kPa (i.e. 1 atmosphere of

Contents 1 Definitions used in the past 2 Definitions in current use 3 Molar volume of a gas 4 References 5 See also 6 External links

Page 1 of 6Standard conditions for temperature and pressure - Wikipedia, the free encyclopedia

11/1/2008http://en.wikipedia.org/wiki/Standard_temperature_and_pressure



absolute pressure). As shown in the following section, that notation is no longer appropriate unless

the specific reference conditions are explicitly stated, since there are currently many different metric

system definitions of what constitutes standard reference conditions.

In the same manner, it is also no longer appropriate to refer to a standard cubic foot (scf) unless the

specific reference conditions are explicitly stated, again because there are currently many different

definitions of the standard reference condition in both the Imperial and the customary U.S. systemsof units. In particular, OPEC and a majority of the natural gas industry in North America have

adopted 60 °F and 14.73 psia as their standard reference conditions for expressing natural gas

volumes and flow rates (rather than the 60 °F and 14.696 psia commonly used previously).

Definitions in current use

There are a great many different definitions of the standard reference conditions currently being

used. Table 1 presents twelve such variations of standard condition definitions - and there are quite a

few others as well.

As shown in the table, the IUPAC (International Union of Pure and Applied Chemistry) currently

defines standard reference conditions as being 0 °C and 1 bar (i.e., 100 kPa) of absolute pressure

rather than the 1 atmosphere (i.e. 101.325 kPa) of absolute pressure used in the past. In fact, the

IUPAC's current definition has been in existence since 1982.[2]

As further shown in the table, the oil and gas industries have to a large extent changed from their

past usage of 60 °F and 14.696 psia to their current usage of 60 °F and 14.73 psia. This is especially

true of the natural gas industry in North America.

For the SATP used in presenting chemical thermodynamic properties (such as those published by the

National Bureau of Standards as included in Table 1) that the pressure is standardized at 1 bar (100kPa) but the temperature may vary and needs to be specified separately.

It should also be noted that 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.

The table makes it quite obvious that it is absolutely necessary to clearly state the temperature and

ressure reference conditions whenever expressing a gas volume or gas volumetric flowrate. It is

equally important to state whether the gas volume is expressed on a dry basis or a wet basis. As

noted in the table, some of the current definitions of the reference conditions include a specificationof the percent relative humidity (% RH).

Table 1: Standard reference conditions in current use

TemperatureAbsolutepressure

Relativehumidity Publishing or establishing entity

°C kPa % RH

0 100.000 IUPAC (present definition)[1]

0 101.325 IUPAC (former definition),[1]

NIST,[3]

ISO10780[4]

15 101.325 0 [4], [5] ISA,[5] ISO 13443,[6] EEA,[7] EGIA[8]





Notes:

101.325 kPa = 1 atmosphere = 1.01325 bar ≈ 14.696 psi 100.000 kPa = 1 bar ≈ 14.504 psi 14.503 psi ≈ 750 mmHg ≈ 100.0 kPa ≈ 1 bar 14.696 psi ≈ 1 atm = 101.325 kPa 14.73 psi ≈ 30 inHg ≈ 1.0156 bar ≈ 101.560 kPa All pressures are absolute pressures (not gauge pressures)

59 °F = 15 °C 60 °F ≈ 15.6 °C dry = 0 percent relative humidity = 0 % RH

The full names of the entities listed in Table 1:

IUPAC: International Union of Pure and Applied Chemistry NIST: National Institute of Standards and Technology ISA: ICAO's International Standard Atmosphere ISO: International Organization for Standardization EEA: European Environment Agency

EGIA: Electricity and Gas Inspection Act (of Canada) EPA: United States Environmental Protection Agency SATP: Standard Ambient Pressure and Temperature CAGI: Compressed Air and Gas Institute SPE: Society of Petroleum Engineers OSHA: U.S. Occupational Safety and Health Administration SCAQMD: California's South Coast Air Quality Management District OPEC: Organization of Petroleum Exporting Countries EIA: U.S. Energy Information Administration Std. Metro: U.S. Army's Standard Metro (used in ballistics) AMCA: Air Movement and Control Association This AMCA standard applies only to air.

Molar volume of a gas

20 101.325 EPA,[9] NIST[10]

25 101.325 EPA[11]

25 100.000 SATP[12]

20 100.000 0CAGI

[13]

15 100.000 SPE[14]

°F psia % RH

60 14.696 SPE,[14] OSHA,[15] SCAQMD[16]

60 14.73 EGIA,[8] OPEC,[17] EIA[18]

59 14.503 78 Army Standard Metro[19]

59 14.696 60 ISO 2314, ISO 3977-2[20]

°F in Hg % RH

70 29.92 0 AMCA,[21] air density = 0.075 lbm/ft³





It is equally as important to indicate the applicable reference conditions of temperature and pressure

when stating the molar volume of a gas[22] as it is when expressing a gas volume or volumetric flowrate. Stating the molar volume of a gas without indicating the reference conditions of temperature

and pressure has no meaning and it can cause much confusion.

The molar gas volumes can be calculated with an accuracy that is usually sufficient by using theuniversal gas law for ideal gases. The usual expression is:

…which can be rearranged thus:

where (in SI metric units):

or where (in customary USA units):

The molar volume of any ideal gas may be calculated at various standard reference conditions as

shown below:

V / n = 8.3145 × 273.15 / 101.325 = 22.414 m³/kmol at 0 °C and 101.325 kPa absolute

pressure V / n = 8.3145 × 273.15 / 100.000 = 22.711 m³/kmol at 0 °C and 100 kPa absolute pressure V / n = 10.7316 × 519.67 / 14.696 = 379.48 ft³/lbmol at 60 °F and 14.696 psia absolute

pressure V / n = 10.7316 × 519.67 / 14.730 = 378.61 ft³/lbmol at 60 °F and 14.73 psia absolute pressure

The technical literature can be very 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 s

which only applies to a specific individual gas. The relationship between the two

constants is R s

= R / M , where M is the molecular weight of the gas.

It may be of interest to note that the US Standard Atmosphere still uses 8.31432 m³·Pa/(mol·K) asthe value of R for all calculations. (See Gas constant)

P = the gas absolute pressure, in Pa

n = number of moles, in mol

V / n = the gas molar volume, in m³/mol

T = the gas absolute temperature, in K

R = the universal gas law constant of 8.3145 m³·Pa/(mol·K)

P = the gas absolute pressure, in psia

n = number of moles, in lbmol

V / n = the gas molar volume, in ft³/lbmol

T = the gas absolute temperature, in °R

R = the universal gas law constant of 10.7316 ft³·psia/(lbmol·°R)





References

1. ^ a b c "Compendium of Terminology", 2nd Edition, 1997, IUPAC Secretariat, Research Triangle Park,P.O. Box 13757, NC, USA (former and present definitions) IUPAC Compendium

2. ^ IUPAC recommended standard pressure of 1 bar in 1982 IUPAC Compendium

3. ^ "NIST Standard Reference Data Base 7 Users Guide", December 1969, NIST, Gaithersburg, MD, USANIST Data Base 74. ^ "Stationary source emissions – Measurement of velocity and volume flow rate of gas streams in ducts",

ISO 10780, International Organization for Standardization, Geneva, Switzerland ISO5. ^ "Handbook of Physics and Chemistry", 56th Edition, pp.F201-F206, CRC Press, Boca Raton, FL, USA6. ^ "Natural gas – Standard reference conditions", ISO 13443, International Organization for

Standardization, Geneva, Switzerland ISO7. ^ "Extraction, First Treatment and Loading of Liquid & Gaseous Fossil Fuels", Emission Inventory

Guidebook B521, Activities 050201 - 050303, September 1999, European Environmental Agency,Copenhagen, Denmark Emission Inventory Guidebook

8. ^ a b "Electricity and Gas Inspection Act", SOR/86-131 (defines a set of standard conditions for Imperialunits and a different set for metric units) Canadian Laws

9. ^ "Standards of Performance for New Sources", 40 CFR--Protection of the Environment, Chapter I, Part60, Section 60.2, 1990 New Source Performance Standards

10. ^ "Design and Uncertainty for a PVTt Gas Flow Standard", Journal of Research of the National Instituteof Standards and Technology, Vol.108, Number 1, 2003 NIST Journal

11. ^ "National Primary and Secondary Ambient Air Quality Standards", 40 CFR--Protection of theEnvironment, Chapter I, Part 50, Section 50.3, 1998 National Ambient Air Standards

12. ^ "Table of Chemical Thermodynamic Properties", National Bureau of Standards (NBS), Journal ofPhysics and Chemical Reference Data, 1982, Vol. 11, Supplement 2.

13. ^ "Glossary", 2002, Compressed Air and Gas Institute, Cleveland, OH, USA Glossary

14. ^ a b "The SI Metric System of Units and SPE Metric Standard (Notes for Table 2.3 on page 25)", June1982, Richardson, TX, USA (defines standard cubic foot and standard cubic meter) SPE

15. ^ "Storage and Handling of Liquefied Petroleum Gases" and "Storage and Handling of AnhydrousAmmonia", 29 CFR--Labor, Chapter XVII--Occupational Safety and Health Administration, Part 1910,

Sect. 1910.110 and 1910.111, 1993 Storage/Handling of LPG16. ^ "Rule 102, Definition of Terms (Standard Conditions)", Amended December 2004, South Coast Air

Quality Management District, Los Angeles, California, USA SCAQMD Rule 10217. ^ "Annual Statistical Bulletin", 2004, Editor-in-chief: Dr. Omar Ibrahim, Organization of the Petroleum

Exporting Countries, Vienna, Austria OPEC Statistical Bulletin18. ^ "Natural Gas Annual 2004", DOE/EIA-0131(04), December 2005, U.S. Department of Energy, Energy

Information Administration, Washington, D.C., USA Natural Gas Annual 200419. ^ "Effects of Altitude and Atmospheric Conditions", Exterior Ballistics Section, Sierra's "Rifle and

Handgun Reloading Manual, 5th Edition", Sedalia, MO, USA Exterior Ballistics20. ^ "Gas turbines – Procurement – Part 2: Standard reference conditions and ratings", ISO 3977-2:1997

and "Gas turbines - Acceptance tests", ISO 2314:1989, Edition 2, International Organization forStandardization, Geneva, Switzerland ISO

21. ^ ANSI/AMCA Standard 210, "Laboratory Methods Of Testing Fans for Aerodynamic PerformanceRating", as implied here: http://www.greenheck.com/pdf/centrifugal/Plug.pdf when accessed on October17, 2007

22. ^ Fundamental Physical Properties: Molar Volumes (CODATA values for ideal gases as listed on aNIST website page)

See also

Standard atmosphere ISO 1 – standard reference temperature for geometric product specifications

External links

"Standard conditions for gases" from the IUPAC Gold Book .





This page was last modified 19:54, 6 January 2008. All text is available under the terms of the GNU Free Documentation License. (See

Copyrights for details.)Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a U.S. registered 501(c)(3) tax-deductible nonprofit charity.

"Standard pressure" from the IUPAC Gold Book . "STP" from the IUPAC Gold Book . "Standard state" from the IUPAC Gold Book .

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