Learn About STP in Chemistry

Learn About STP in Chemistry STP in chemistry is the abbreviation for Standard Temperature and Pressure. STP most commonly is used when performing calculations on gases, such as gas density. The standard temperature is 273 K (0 ° Celsius or 32 ° Fahrenheit) and the standard pressure is 1 atm pressure. This is the freezing point of pure water at sea level atmospheric pressure. At STP, one mole of gas occupies 22.4 L of volume (molar volume). Note the International Union of Pure and Applied Chemistry (IUPAC) applies a more stringent standard of STP as  a temperature of 273.15 K (0  °C, 32  °F) and an absolute pressure of exactly 100,000 Pa (1 bar, 14.5 psi, 0.98692 atm). This is a change from their earlier standard (changed in 1982) of  0  °C and 101.325 kPa (1 atm). Key Takeaways: STP or Standard Temperature and Pressure STP is the abbreviation for Standard Temperature and Pressure. However, the standard is defined differently by various groups.STP values are most often cited for gases because their characteristics change dramatically with temperature and pressure.One common definition of STP is a temperature of 273 K  (0 ° Celsius or 32 ° Fahrenheit) and the standard pressure of 1 atm. Under these conditions, one mole of a gas occupies 22.4 L.Because the standard varies by industry, its good practice to state temperature and pressure conditions for measurements and not just say STP. Uses of STP Standard reference conditions are important for expressions of fluid flow rate and the volumes of liquids and gases, which are highly dependent on temperature and pressure. STP commonly is used when standard state conditions are applied to calculations. Standard state conditions, which include standard temperature and pressure, may be recognized in calculations by the superscript circle. For example, ΔS ° refers to the change in entropy at STP. Other Forms of STP Because laboratory conditions rarely involve STP, a common standard is standard ambient temperature and pressure or SATP, which is  a temperature of 298.15 K (25  °C, 77  °F) and an absolute pressure of exactly 1 atm (101,325 Pa, 1.01325 bar). The International Standard Atmosphere or ISA and the U.S. Standard Atmosphere are standards used in the fields of fluid dynamics and aeronautics to specify temperature, pressure, density, and the speed of sound for a range of altitudes at the mid-latitudes. The two sets of standards are the same at altitudes up to 65,000 feet above sea level. The National Institute of Standards and Technology (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) for STP. The Russian  State Standard GOST 2939-63 uses the standard conditions of 20  °C (293.15 K), 760 mmHg (101325 N/m2) and zero humidity.  The International Standard Metric Conditions for natural gas are 288.15 K (15.00  °C; 59.00  °F) and 101.325 kPa. The International Organization for Standardization (ISO) and the United States Environmental Protection Agency (US EPA) both set their own standards, too. Correct Use of the Term STP Even though STP is defined, you can see the precise definition depends on the committee that set the standard! Therefore, rather than citing a measurement as performed at STP or standard conditions, its always best to explicitly state the temperature and pressure reference conditions. This avoids confusion. In addition, it is important to state the temperature and pressure for the molar volume of a gas, rather than citing STP as the conditions. When calculated molar volume, one should state whether the calculation used the ideal gas constant R or the specific gas constant Rs. The two constants are related where Rs R / m, where m is the molecular mass of a gas. Although STP is most commonly applied to gases, many scientists try to perform experiments at STP to SATP to make it easier to replicate them without introducing variables. Its good lab practice to always state the temperature and pressure or to at least record them in case they turn out to be important. Sources Doiron, Ted (2007). 20  °C – A Short History of the Standard Reference Temperature for Industrial Dimensional Measurements. National Institute of Standards and Technology. Journal of Research of the National Institute of Standards and Technology.McNaught, A. D.; Wilkinson, A. (1997). Compendium of Chemical Terminology, The Gold Book (2nd ed.). Blackwell Science. ISBN 0-86542-684-8.Natural gas – Standard reference conditions (ISO 13443). Geneva, Switzerland: International Organization for Standardization. 1996.Weast, Robert C. (Editor) (1975). Handbook of Physics and Chemistry (56th ed.). CRC Press. pp. F201–F206. ISBN 0-87819-455-X.