Standard conditions for temperature and pressure

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Standard conditions for temperature and pressure

"Standard conditions" redirects here. For the standard state of a substance, see standard state

Standard state

In chemistry, the standard state of a material is a reference point used to calculate its properties under different conditions. In principle, the choice of standard state is arbitrary, although the International Union of Pure and Applied Chemistry recommends a conventional set of standard states for general use....
.

In physical science
Physical science

Physical science is an encompassing term for the branches of natural science and science that study non-living systems, in contrast to the biology sciences....
s, standard conditions for temperature and pressure are standard
Standard

A technical standard is an established norm or requirement. It is usually a formal document that establishes uniform engineering or technical criteria, methods, processes and practices....
sets of conditions for experimental measurements, 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
International Union of Pure and Applied Chemistry

The International Union of Pure and Applied Chemistry is a non-governmental organization established in 1919 for the advancing of chemistry. Its members are national chemistry societies....
(IUPAC) and the National Institute of Standards and Technology
National Institute of Standards and Technology

The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory which is a non-regulatory agency of the United States Department of Commerce....
(NIST) but are far from being universal standards.

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"Standard conditions" redirects here. For the standard state of a substance, see standard state
Standard state

In chemistry, the standard state of a material is a reference point used to calculate its properties under different conditions. In principle, the choice of standard state is arbitrary, although the International Union of Pure and Applied Chemistry recommends a conventional set of standard states for general use....
.

In physical science
Physical science

Physical science is an encompassing term for the branches of natural science and science that study non-living systems, in contrast to the biology sciences....
s, standard conditions for temperature and pressure are standard
Standard

A technical standard is an established norm or requirement. It is usually a formal document that establishes uniform engineering or technical criteria, methods, processes and practices....
sets of conditions for experimental measurements, 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
International Union of Pure and Applied Chemistry

The International Union of Pure and Applied Chemistry is a non-governmental organization established in 1919 for the advancing of chemistry. Its members are national chemistry societies....
(IUPAC) and the National Institute of Standards and Technology
National Institute of Standards and Technology

The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory which is a non-regulatory agency of the United States Department of Commerce....
(NIST) but are far from being universal standards. Other organizations have established a variety of alternative definitions for their standard reference conditions. The current version of IUPAC's standard is a temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
of 0 °C (273.15 K
Kelvin

The kelvin is a Units of measurement of temperature and is one of the seven SI base units. The Kelvin scale is a Thermodynamic temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero ....
, 32 °F) and an absolute pressure of 100 kPa
KPA

KPA may refer to:* Kenya Ports Authority* Kilopascal , a unit of pressure* Known-plaintext attack, a method of cryptanalysis* Korean People's Army...
(14.504 psi), while NIST's version is a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 101.325 kPa (14.696 psi).

In industry
Industry

An industry is the manufacturing of a Good or Service within a category. Although industry is a broad term for any kind of economic production, in economics and urban planning industry is a synonym for the secondary sector, which is a type of economic activity involved in the manufacturing of raw materials into goods and products....
and commerce
Commerce

Commerce is a division of trade or production, costs, and pricing which deals with the Trade of goods and service from production, costs, and pricing to final consumer....
, 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 and liquids 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.

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 0 °C (273.15 K
Kelvin

The kelvin is a Units of measurement of temperature and is one of the seven SI base units. The Kelvin scale is a Thermodynamic temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero ....
) and 101.325 kPa
KPA

KPA may refer to:* Kenya Ports Authority* Kilopascal , a unit of pressure* Known-plaintext attack, a method of cryptanalysis* Korean People's Army...
(1 atm
Atmosphere (unit)

The standard atmosphere is an international reference pressure defined as 101,325 Pascal and formerly used as unit of pressure . For practical purposes it has been replaced by the Bar which is 100,000 Pa....
). During those same years, the most commonly used standard reference conditions for people using the Imperial unit
Imperial unit

Imperial units or the imperial system is a system of units, first defined in the British Weights and Measures Act of 1824, later refined and reduced....
s or U.S. customary units was 60 °F
Fahrenheit

Fahrenheit is a temperature scale named after the physicist Daniel Gabriel Fahrenheit , who proposed it in 1724. Today, the scale has largely been replaced by the Celsius scale; it is still in use for non-scientific purposes in the United States and a few other countries such as Belize....
(520 °R) and 14.696 psi (1 atm) because it was almost universally used by the oil and gas industries worldwide. However, the above two definitions are no longer the most commonly used in either system of units.

Current use

Many different definitions of standard references 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, such as IUPAC which currently defines standard reference conditions as being 0 °C and 100 kPa (1 bar) of pressure rather since 1982, in contrast to their old standard of 0 °C and 101.325 kPa (1 atm). Another example is from the oil industry. While a standard of 60 °F and 14.696 psi was used in the past, the current usage (particularly in North America) is predominantly of 60 °F and 14.73 psi.

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. Also, the International Organization for Standardization
International Organization for Standardization

The International Organization for Standardization , widely known as ISO , is an international standard-setting body composed of representatives from various national standards organizations....
(ISO), the United States Environmental Protection Agency
United States Environmental Protection Agency

The U.S. Environmental Protection Agency is an List of United States federal agencies of the federal government of the United States charged to Regulation of chemicals and protect human health by safeguarding the natural environment: air, water, and land....
(EPA) and National Institute of Standards and Technology
National Institute of Standards and Technology

The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory which is a non-regulatory agency of the United States Department of Commerce....
(NIST) each have more than one definition of standard reference conditions in their various standards and regulations.

The SATP used for presenting chemical thermodynamic properties (such as those published by the National Bureau of Standards) is standardized at 100 kPa (1 bar) but the temperature may vary and usually needs to be specified separately if complete information is desired (see standard state
Standard state

In chemistry, the standard state of a material is a reference point used to calculate its properties under different conditions. In principle, the choice of standard state is arbitrary, although the International Union of Pure and Applied Chemistry recommends a conventional set of standard states for general use....
). Some standards are specified at certain humidity level
Relative humidity

Relative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water....
.

Table 1: Standard reference conditions in current use
Temperature Absolute pressure Relative humidity Publishing or establishing entity
°C kPa % RH
0 100.000 IUPAC (present definition)
0 101.325 IUPAC (former definition), NIST
National Institute of Standards and Technology

The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory which is a non-regulatory agency of the United States Department of Commerce....
, ISO 10780
15 101.325 0 ICAO's ISA
International Standard Atmosphere

The International Standard Atmosphere is an atmospheric models of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes....
, ISO 13443, EEA
European Environment Agency

European Environment Agency , agency of the European Union devoted to establishing a monitoring network for the monitoring of the European environment....
, EGIA
20 101.325 EPA
United States Environmental Protection Agency

The U.S. Environmental Protection Agency is an List of United States federal agencies of the federal government of the United States charged to Regulation of chemicals and protect human health by safeguarding the natural environment: air, water, and land....
, NIST
25 101.325 EPA
25 100.000 SATP
20 100.000 0 CAGI
Compressed Air and Gas Institute

Compressed Air and Gas Institute or CAGI is an industry association located in Cleveland, Ohio. It was founded in 1915. CAGI is representing manufacturers of compressed air system equipment, including air compressors, blowers, pneumatic tools and air and gas drying and filtration equipment....
15 100.000 SPE
Society of Petroleum Engineers

The Society of Petroleum Engineers is a professional organization whose mission is to collect, disseminate, and exchange technical knowledge concerning the oil exploration, development and production of oil and gas resources and related technologies for the public benefit and to provide opportunities for professionals to enhance their techni...
20 101.3 50 ISO 5011
°F psi % RH
60 14.696 SPE, U.S. OSHA
Occupational Safety and Health Administration

The United States Occupational Safety and Health Administration is an agency of the United States Department of Labor. It was created by Congress of the United States under the Occupational Safety and Health Act, signed by President Richard M....
, SCAQMD
60 14.73 EGIA, OPEC, U.S. EIA
Energy Information Administration

The United States Energy Information Administration , created by United States Congress in 1977, is the independent statistical agency within the United States Department of Energy....
59 14.503 78 U.S. Army Standard Metro
59 14.696 60 ISO 2314, ISO 3977-2
°F in Hg % RH
70 29.92 0 AMCA
Air Movement and Control Association

The Air Movement and Control Association International, Inc. is a nonprofit organization that creates standards for, tests, and rates Heating, Ventilating, and Air Conditioning equipment....
, air density = 0.075 lbm/ft³. This AMCA standard applies only to air.

Notes:
EGIA: Electricity and Gas Inspection Act (of Canada)
SATP: Standard Ambient Pressure and Temperature
SCAQMD: California's South Coast Air Quality Management District

International Standard Atmosphere

In aeronautics
Aeronautics

File:An-225 Mriya.jpgFile:Atlantis on Shuttle Carrier Aircraft.jpgFile:Typhoon f2 zj910 arp.jpgAeronautics is the science involved with the study, design, and manufacture of flight-capable machines, or the techniques of operating aircraft....
and fluid dynamics
Fluid dynamics

In physics, fluid dynamics is the sub-discipline of fluid mechanics dealing with fluid flow — the natural science of fluids in motion....
the term "International Standard Atmosphere
International Standard Atmosphere

The International Standard Atmosphere is an atmospheric models of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes....
" is often used to denote the variation of the principal thermodynamic variables (pressure, temperature, density, etc.) of the atmosphere with altitude at mid latitudes.

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. The concept of "standard laboratory conditions" taught as part of the New South Wales high school chemistry syllabus is 25 °C at 100 kPa.

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 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 no meaning and it can cause confusion.

The molar gas volumes can be calculated with an accuracy that is usually sufficient by using the universal 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
V/n = 8.3145 × 273.15 / 100.000 = 22.711 m³/kmol at 0 °C and 100 kPa
V/n = 8.3145 × 298.15 / 101.325 = 24.466 m³/kmol at 25 °C and 101.325 kPa
V/n = 8.3145 × 298.15 / 100.000 = 24.790 m³/kmol at 25 °C and 100 kPa
V/n = 10.7316 × 519.67 / 14.696 = 379.48 ft³/lbmol at 60 °F and 14.696 psi
V/n = 10.7316 × 519.67 / 14.730 = 378.61 ft³/lbmol at 60 °F and 14.73 psi

The technical literature can be 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.

The US Standard Atmosphere
US Standard Atmosphere

The U.S. Standard Atmosphere is a series of models that define values for Earth's atmosphere temperature, density, Atmospheric pressure and other properties over a wide range of altitudes....
uses 8.31432 m³·Pa/(mol·K) as the value of R for all calculations. (See Gas constant
Gas constant

The gas constant is a physical constant which is featured in a large number of fundamental equations in the physical sciences, such as the ideal gas law and the Nernst equation....
)

See also

Atmospheric models
Atmospheric models

Static atmospheric models describe how the ideal gas properties of an atmosphere change, primarily as a function of altitude.For example, the US Standard Atmosphere is essentially a table of values for air temperature, pressure, and mass density, as a function of altitude above sea level....
ISO 1
ISO 1

International Standard ISO 1 specifies the standard reference temperature for geometrical product specification and verification to be 20 ?C, which is equal to 293.15 K and 68 ?F....
– standard reference temperature for geometric product specifications
Standard state
Standard state

In chemistry, the standard state of a material is a reference point used to calculate its properties under different conditions. In principle, the choice of standard state is arbitrary, although the International Union of Pure and Applied Chemistry recommends a conventional set of standard states for general use....

External links

from the IUPAC Gold Book.
from the IUPAC Gold Book.
from the IUPAC Gold Book.
from the IUPAC Gold Book.