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In chemistry, IUPAC changed its definition of standard temperature and pressure in 1982: [1] [2] Until 1982, STP was defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 1 atm (101.325 kPa).
The standard state should not be confused with standard temperature and pressure (STP) for gases, [4] nor with the standard solutions used in analytical chemistry. [5] STP is commonly used for calculations involving gases that approximate an ideal gas, whereas standard state conditions are used for thermodynamic calculations. [6]
Materials that exist primarily in the gas phase at STP (i.e., "evaporates more than 95% by weight within six months under ambient evaporation testing conditions" [3]) are referred to as "volatile." [ 1 ] Many natural and man-made ( anthropogenic ) materials are stable in two states at STP, earning them the title "semivolatile."
Until 1982, STP was defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of 101.325 kPa (1 atm). Since 1982, STP is defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of 100 kPa (1 bar). Conversions between each volume flow metric are calculated using the following formulas: Prior to 1982,
The second table gives the most stable structure of each element at its melting point. (H, He, N, O, F, Ne, Cl, Ar, Kr, Xe, and Rn are gases at STP; Br and Hg are liquids at STP.) Note that helium does not have a melting point at atmospheric pressure, but it adopts a magnesium-type hexagonal close-packed structure under high pressure.
In this page it's said: "In chemistry, the term standard temperature and pressure (abbreviated STP) denotes an exact reference temperature of 0°C (273.15 K) and pressure of 1 atm (defined as 101325 Pa)."
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The superscript Plimsoll on this symbol indicates that the process has occurred under standard conditions at the specified temperature (usually 25 °C or 298.15 K). Standard states are defined for various types of substances. For a gas, it is the hypothetical state the gas would assume if it obeyed the ideal gas equation at a pressure of 1 bar.