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Standard temperature and pressure (STP) are
standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metrology), an object that bears a defined relationship to a unit of ...
sets of conditions for experimental measurements to be 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 The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science Council (ISC). IUPAC i ...
(IUPAC) and the
National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is a physical sciences laboratory and a non-regulatory agency of the United States Department of Commerce. Its mission is to promote innovation and industrial competitiveness. NIST's act ...
(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 changed the definition of standard temperature and pressure in 1982: * Until 1982, STP was defined as a
temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact with another that is ...

temperature
of 273.15 
K
K
(0 °C, 32 °F) and an
absolute pressure Pressure measurement is the analysis of an applied force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that st ...
of exactly 1 
atm ATM or atm often refers to: * Atmosphere (unit) or atm, a unit of atmospheric pressure * Automated teller machine, a cash dispenser or cash machine ATM or atm may also refer to: Computing * ATM (computer), a ZX Spectrum clone developed in Mos ...
(101.325 
kPa The pascal (symbol: Pa) is the SI derived unit SI derived units are units of measurement ' Measurement is the number, numerical quantification (science), quantification of the variable and attribute (research), attributes of an object or event, ...
). * Since 1982, STP is defined as a
temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact with another that is ...

temperature
of 273.15 
K
K
(0 °C, 32 °F) and an
absolute pressure Pressure measurement is the analysis of an applied force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that st ...
of exactly 105  Pa (100 kPa, 1 
bar Bar or BAR may refer to: Food *Bar (establishment) A bar is a long raised narrow table or bench designed for dispensing beer or other alcoholic beverage, alcoholic drinks. They were originally chest high, and a bar, often brass, ran the lengt ...
). STP should not be confused with the
standard state In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they under ...
commonly used in thermodynamic evaluations of the
Gibbs energy In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governe ...
of a reaction.
NIST The National Institute of Standards and Technology (NIST) is a physical sciences laboratory and a non-regulatory agency of the United States Department of Commerce. Its mission is to promote innovation and industrial competitiveness. NIST's acti ...
uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa). 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
K
(25° C, 77°
F
F
) and 1
bar Bar or BAR may refer to: Food *Bar (establishment) A bar is a long raised narrow table or bench designed for dispensing beer or other alcoholic beverage, alcoholic drinks. They were originally chest high, and a bar, often brass, ran the lengt ...
(14.5038 psi, 100 kPa). NIST also uses "15 °C (60 °F)" for the temperature compensation of refined petroleum products, despite noting that these two values are not exactly consistent with each other. The International Standard Metric Conditions for natural gas and similar fluids are and 101.325 kPa. In
industry Industry may refer to: Economics * Industry (economics) In macroeconomics, an industry is a branch of an economy that produces a closely related set of raw materials, goods, or services. For example, one might refer to the wood industry ...
and
commerce Commerce is the exchange of goods and services, especially on a large scale. Etymology The English-language word ''commerce'' has been derived from the Latin word ''commercium'', from ''com'' ("together") and ''merx'' ("merchandise"). History ...

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 In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior through ...
(the volumes of gases vary significantly with temperature and pressure):
standard cubic meters per second Flow measurement is the quantification of bulk fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Fluids are a Phase (matter), phase of matter a ...
(Sm3/s), and normal cubic meters per second (Nm3/s). However, 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 Normal conditions are a restriction on philosophical Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, existence, knowledge Knowledge is a familiarity, awareness, or understanding ...
", 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


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 and . During those same years, the most commonly used standard reference conditions for people using the
imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imperial, Nebraska * Imperial, Pennsylvania * Imperial, Texas * ...
or U.S. customary systems was 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). 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). 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 A standard cubic foot (scf) is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatric ...
. Also, the
International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization develops and publishe ...
(ISO), the
United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government The federal government of the United States (U.S. federal government) is the national government of the United States ...
(EPA) and
National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is a physical sciences laboratory and a non-regulatory agency of the United States Department of Commerce. Its mission is to promote innovation and industrial competitiveness. NIST's act ...
(NIST) each have more than one definition of standard reference conditions in their various standards and regulations. Abbreviations: * EGIA: Electricity and Gas Inspection Act (of Canada) * SATP: Standard Ambient Temperature and Pressure * SCF: Standard Cubic Foot


International Standard Atmosphere

In
aeronautics Aeronautics is the science or art involved with the study, design, and manufacturing of air flight Flight or flying is the process by which an object (physics), object motion (physics), moves through a space without contacting any planetary ...
and
fluid dynamics In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. " ...
the "
International Standard Atmosphere The International Standard Atmosphere (ISA) is a static atmospheric model of how the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗ ...

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

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 A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which science, scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of sett ...

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 New South Wales (abbreviated as NSW) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper ...
,
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, smal ...

Australia
use 25 °C at 100 kPa for standard laboratory conditions.
ASTM International ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization A standards organization, standards body, standards developing organization (SDO), or standards setting organization (SS ...
has published
Standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metrology), an object that bears a defined relationship to a unit of ...
ASTM E41- Terminology Relating to Conditioning and hundreds of special conditions for particular materials and
test method A test method is a methodology, method for a test in science or engineering, such as a physical test, chemical test, or statistical hypothesis testing, statistical test. It is a definitive procedure that produces a test result. In order to ensure ac ...
s. Other
standards organization A standards organization, standards body, standards developing organization (SDO), or standards setting organization (SSO) is an organization whose primary function is developing, coordinating, promulgating, revising, amending, reissuing, interpre ...
s 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 In chemistry and related fields, the molar volume, symbol ''V''m, or \tilde V of a substance is the occupied volume divided by the amount of substance at a given temperature and pressure. It is equal to the molar mass (''M'') divided by the mass de ...
of a gas 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 Isotherms of an ideal gas. The curved lines represent the relationship between pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), k ...

ideal gas law
. The molar volume of any ideal gas may be calculated at various standard reference conditions as shown below: * ''V''m = 8.3145 × 273.15 / 101.325 = 22.414  dm3/mol at 0 °C and 101.325 kPa * ''V''m = 8.3145 × 273.15 / 100.000 = 22.711 dm3/mol at 0 °C and 100 kPa * ''V''m = 8.3145 × 298.15 / 101.325 = 24.466 dm3/mol at 25 °C and 101.325 kPa * ''V''m = 8.3145 × 298.15 / 100.000 = 24.790 dm3/mol at 25 °C and 100 kPa * ''V''m = 10.7316 × 519.67 / 14.696 = 379.48 ft3/lbmol at 60 °F and 14.696 psi (or about 0.8366 ft3/gram mole) * ''V''m = 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 The gas constant (also known as the molar gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol or . It is equivalent to the Boltzmann constant, but expressed in units of energy per temperature, temperature increme ...
''R'', or the specific gas constant ''R''s. The relationship between the two constants is ''R''s = ''R'' / ''m'', where ''m'' is the
molecular mass The molecular mass (''m'') is the mass of a given molecule: it is measured in dalton (unit), daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The r ...
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.''U.S. Standard Atmosphere, 1976''
U.S. Government Printing Office, Washington, D.C., 1976.


See also

* *
ISO 1 ISO 1 is an international standard set by the International Organization for Standardization that specifies the standard reference temperature for geometrical product specification and verification. The temperature is fixed at 20 °C, which is ...
 – standard reference temperature for geometric product specifications *
Reference atmospheric model A reference atmospheric model describes how the ideal gas properties (namely: pressure, temperature, density, and molecular weight) of an atmosphere change, primarily as a function of altitude, and sometimes also as a function of latitude In ...
*
Room temperature Colloquially, room temperature is the range of air temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat ...
*
Standard sea levelStandard sea-level conditions (SSL), also known as sea-level standard (SLS), defines a set of atmospheric conditions for physical calculations. The term "standard sea level Mean sea level (MSL) (often shortened to sea level) is an mean, average l ...
*
Standard state In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they under ...


Explanatory notes


References

{{Reflist


External links


"Standard conditions for gases"
from the
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the authoritative power over chemistr ...
''Gold Book''.
"Standard pressure"
from the
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the authoritative power over chemistr ...
''Gold Book''.
"STP"
from the
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the authoritative power over chemistr ...
''Gold Book''.
"Standard state"
from the
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the authoritative power over chemistr ...
''Gold Book''. Atmospheric thermodynamics Aerodynamics Engineering thermodynamics Gases Measurement Physical chemistry Standards Thermodynamics