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 100.00 kPa (14.504 psi, 0.987 atm, 1.000 bar).^[1] An unofficial, but commonly used standard is standard ambient temperature and pressure (SATP) as a temperature of 298.15 K (25 °C, 77 °F) and an absolute pressure of 100.0 kPa (14.504 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 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 288.15 K (15.00 °C; 59.00 °F) and 101.325 kPa.^[2]

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 1
- Past use 1.1
- Current use 1.2
International Standard Atmosphere 2
Standard laboratory conditions 3
Molar volume of a gas 4
See also 5
Notes 6
References 7
External links 8

Definitions

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 15 °C (288.15 K; 59.00 °F) and 101.325 kPa (1.00 atm; 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. 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).^[3]

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.^[4]^[5]^[6] Also, 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.

**Standard reference conditions in current use**
Temperature	Absolute pressure	Relative humidity	Publishing or establishing entity
°C	kPa	%	Publishing or establishing entity
0	100.000		IUPAC (STP)^[1]
0	101.325		NIST,^[7] ISO 10780,^[8] formerly IUPAC^[1]
15	101.325	0^[2]^[9]	ICAO's ISA,^[9] ISO 13443,^[2] EEA,^[10] EGIA^[11]
20	101.325		EPA,^[12] NIST^[13]
22	101.325	20-80	American Association of Physicists in Medicine^[14]
25	101.325		EPA^[15]
25	100.000		SATP^[16]
20	100.000	0	CAGI^[17]
15	100.000		SPE^[18]
20	101.3	50	ISO 5011^[19]
°F	psi	%
60	14.696		SPE,^[18] U.S. OSHA,^[20] SCAQMD^[21]
60	14.73		EGIA,^[11] OPEC,^[22] U.S. EIA^[23]
59	14.503	78	U.S. Army Standard Metro^[24]^[1]
59	14.696	60	ISO 2314,^[25] ISO 3977-2^[26]
°F	in Hg	%
70	29.92	0	AMCA,^[27]^[2] air density = 0.075 lbm/ft³. This AMCA standard applies only to air.
59	29.92		Federal Aviation Administration (FAA)^[28]

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.

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.^[29]

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^[30] 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 R_s. The relationship between the two constants is R_s = 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.^[31]

Notes

^ 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.
^ 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 32 °F (0 °C).

References

^ ^a ^b ^c A. D. McNaught and A. Wilkinson (1997). IUPAC. Compendium of Chemical Terminology (2nd ed.). Oxford: Blackwell Scientific Publications.
^ ^a ^b ^c Natural gas – Standard reference conditions (ISO 13443). Geneva, Switzerland: International Organization for Standardization. 1996.
^ A. D. McNaught, A. Wilkinson (1997). Compendium of Chemical Terminology, The Gold Book (2nd ed.). Blackwell Science.
^
^
^
^
^
^ ^a ^b Robert C. Weast (Editor) (1975). Handbook of Physics and Chemistry (56th ed.). CRC Press. pp. F201–F206.
^ Extraction, First Treatment and Loading of Liquid & Gaseous Fossil Fuels (Emission Inventory Guidebook B521, Activities 050201 – 050303) (PDF). Copenhagen, Denmark: European Environmental Agency. September 1999.
^ ^a ^b "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
^ "Standards of Performance for New Sources", 40 CFR—Protection of the Environment, Chapter I, Part 60, Section 60.2, 1990 New Source Performance Standards
^ "Design and Uncertainty for a PVTt Gas Flow Standard" (PDF). Journal of Research of the National Institute of Standards and Technology 108 (1). 2003.
^ "AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams" (PDF). Medical Physics 26 (9). 1999.
^ "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
^ National Bureau of Standards (NBS) (1982). "Table of Chemical Thermodynamic Properties". Journal of Physics and Chemical Reference Data 11 (Supplement 2).
^ "Glossary". Cleveland, OH, USA: Compressed Air and Gas Institute. 2002.
^ ^a ^b "The SI Metric System of Units and SPE Metric Standard" (PDF). Society of Petroleum Engineers. 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.
^ Air Intake Filters (ISO 5011:2002). Geneva, Switzerland: International Organization for Standardization. 2002.
^ "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
^ "Rule 102, Definition of Terms (Standard Conditions)", Amended December 2004, South Coast Air Quality Management District, Los Angeles, California, USA SCAQMD Rule 102
^ Omar Ibrahim, ed. (2004). "Annual Statistical Bulletin" (PDF). Vienna, Austria: Organization of the Petroleum Exporting Countries.
^ Energy Information Administration (December 2005). "Natural Gas Annual 2004 (DOE/EIA-0131(04))" (PDF). Washington, D.C., USA: U.S. Department of Energy.
^ Sierra Bullets L.P. "Chapter 3 – Effects of Altitude and Atmospheric Conditions (Exterior Ballistics Section)". Rifle and Handgun Reloading Manual (5 ed.). Sedalia, MO, USA-.
^ Gas turbines – Acceptance tests (ISO 2314:1989) (2 ed.). Geneva, Switzerland: International Organization for Standardization. 1989.
^ Gas turbines – Procurement – Part 2: Standard reference conditions and ratings (ISO 3977-2:1997). Geneva, Switzerland: International Organization for Standardization. 1997.
^ 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
^ "Chapter 3, Principles of Flight". Pilot's Handbook of Aeronautical Knowledge (PDF). Federal Aviation Administration.
^ Peter Gribbon (2001). Excel HSC Chemistry Pocket Book Years 11–12. Pascal Press.
^ "Fundamental Physical Properties: Molar Volumes (CODATA values for ideal gases)".
^ U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C., 1976.

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.

Standard conditions for temperature and pressure