Standard conditions for temperature and pressure

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Standard conditions for temperature and pressure are the set of default conditions for experimental measurements to be set to allow comparisons to be made between different data sets. The most widely used standard is the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST) standards, although this standard is not universally accepted. Other organizations have established various alternative definitions for their standard reference conditions.

In chemistry, IUPAC has changed the definition of temperature and standard pressure ( STP ) in 1982:

• Until 1982, STP was defined as a temperature of 273.15 K (0 Â ° C, 32 Â ° F) and an absolute pressure of exactly 1 atm (1.01325 ÃÆ' â € "10 ^{5 Ã, Pa).}
• Since 1982, STP is defined as a temperature of 273.15 K (0 Â ° C, 32 Â ° F) and an absolute pressure of exactly 10 ⁵ Pa (100 kPa, 1 bar).

STP should not be confused with the standard state commonly used in the evaluation of thermodynamic Gibbs energy reactions.

NIST uses temperatures of 20 Ã, Â ° C (293.15 Ã, Â ° K, 68 Ã, Â ° F) and absolute pressure of 1 atm (14,696Ã, psi, 101,325 kPa). This standard is also called normal temperature and pressure (abbreviated NTP ).

International Standard Metric conditions for natural gas and similar fluids are 288.15 K (15,00 Â ° C; 59,00 Â ° F) and 101,325 kPa.

In industry and commerce, standard conditions for temperature and pressure are often required to define standard reference conditions for expressing gas and liquid volumes and related quantities such as volumetric flow rate (gas volume varies significantly with temperature and pressure) - standard cubic meters per second (< b> sm3/s ), and normal cubic meters per second ( nm3/s ). However, many technical publications (books, journals, advertisements for equipment and machines) simply state "standard conditions" without specifying them, often leading to confusion and error. Good practice always incorporates temperature reference and pressure conditions.

Video Standard conditions for temperature and pressure

Definition

Past Usage

Prior to 1918, many professionals and scientists using a unit metric system defined standard reference conditions for temperature and pressure to express the gas volume as 15 ° C (288.15 Â ° K; 59,00 Â ° F) and 101.325 kpa (1, 00 atm; 760Ã, Torr). During the same years, the most common standard reference conditions used for people using customary or customary systems are 60 ° F (15.56 Â ° C; 288.71 K) and 14.696 psi (1 atm) for almost universally used by the oil and gas industry worldwide. The above definition is no longer the most commonly used in both unit systems.

Current use

Many different definitions of standard reference conditions are currently being used by organizations around the world. The table below lists some 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 0 Â ° C and 100 kpa (1 bar), in contrast to the old standard 0 Â ° C and 101.325 kPa (1 atm).

Natural gas companies in Europe, Australia and South America have adopted 15Ã, ° C (59Ã,  ° F) and 101,325 kPa (14,696Ã, psi) as their standard gas volume reference conditions, used as the base values ​​for defining cubic standards meters. Also, the International Organization for Standardization (ISO), the United States Environmental Protection Agency (EPA) and the National Institute of Standards and Technology (NIST) each have more than one definition of standard reference conditions in their various standards and regulations.

Note:

• EGIA: Electrical and Gas Inspection Act (Canada)
• SATP: Standard Ambient Temperature and Pressure
• SCF: Standard Cubic Feet

Maps Standard conditions for temperature and pressure

International Standard Atmosphere

In aeronautics and fluid dynamics, "International Standard Atmosphere" (ISA) is a specification of pressure, temperature, density, and speed of sound at each altitude. The International Standard Atmosphere represents the atmospheric conditions in the middle latitudes. In the US, this information is determined by the US Atmospheric Standards identical to the "International Standard Atmosphere" at all elevations up to 65,000 feet above sea level.

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Standard laboratory conditions

Due to the fact that many standard temperature and pressure definitions differ in temperature significantly from standard laboratory temperatures (eg, 0 Â ° C vs. ~ 25 Â ° C), references are often made to â € Å" standard laboratory conditionsâ € (a term deliberately created ). chosen to be different from the term "standard conditions for temperature and pressure", despite the close semantic identity when interpreted literally). However, what is meant by "standard" laboratory temperatures and pressures is bound to geography, given that different parts of the world differ in climate, altitude and rate of heat/cooling in the workplace. For example, schools in New South Wales, Australia use 25Ã, Â ° C at 100Ã, kPa for standard laboratory conditions. ASTM International has published the ASTM E41- Terminology Standard Relating to Conditioning and hundreds of special conditions for specific materials and test methods. Other standard organizations also have special standard testing requirements.

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Molar gas volume

It is equally important to indicate the applicable temperature reference and pressure conditions when stating the molar volume of the gas as when expressing a gas volume or volumetric flow rate. Stating the molar volume of the gas without indicating the temperature and pressure reference conditions has very little meaning and can cause confusion.

The molar volume of the gas around the STP and atmospheric pressure can be calculated with an accuracy which is usually sufficient by using an ideal gas law. The molar volume of any ideal gas can be calculated under various standard reference conditions as shown below:

• V _m = 8.3145 ÃÆ'â € "273.15/101.325 = 22.414 dm ³ /mol at 0 Ã, Â ° C and 101,325 Ã, kPa
• V _m = 8.3145 ÃÆ'â € "273.15/100.000 = 22.711 dm ³ /mol at 0, c and 100Ã, kPa
• V _m = 8.3145 ÃÆ'â € "298.15/101.325 = 24.466 dm ³ /mol at 25 Ã, Â ° C and 101,325 kPa
• V _m = 8.3145 ÃÆ'â € "298.15/100.000 = 24.790 dm ³ /mol at 25Ã, Â ° C and 100Ã, kPa
• V _m = 10.7316 ÃÆ'â € "519.67/14.696 = 379.48Ã, ft ³ /lbmol at 60Ã, Â ° F and 14,696 Ã, psi (or about 0.8366 ft ³ /gram mol)
• V _m = 10.7316 ÃÆ'â € "519.67/14.730 = 378.61Ã, ft ³ /lbmol at 60Ã, Â ° F and 14.73 psi

The technical literature can be confusing as many authors fail to explain whether they use the ideal gas constants R , or certain gas constants R _s . The relationship between two constants is R _s = R / m , where m is the mass of the gas molecule.

US Standard Atmosphere (USSA) uses 8.31432 m ³ Ã, Â · Pa/(molÃ, Â · K) as the value R . However, USSA, 1976 does recognize that this value is inconsistent with the values ​​of Avogadro's constant and Boltzmann's constant.

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See also

• Atmosphere model
• Environmental space
• ISO 1Ã, - standard reference temperature for geometric product specifications
• Standard Dry Air
• Standard conditions
• Standard sea level
• Room temperature

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Note

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References

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External links

• "Standard conditions for gas" from IUPAC Golden Book .
• "Standard Pressure" from IUPAC Golden Book .
• "STP" from IUPAC Golden Book .
• "Standard status" of IUPAC Golden Book .

Source of the article : Wikipedia