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Since 1982, STP has been defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 10 5 Pa (100 kPa, 1 bar). NIST uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa). [3] This standard is also called normal temperature and pressure (abbreviated as NTP).
The pascal (Pa) or kilopascal (kPa) as a unit of pressure measurement is widely used throughout the world and has largely replaced the pounds per square inch (psi) unit, except in some countries that still use the imperial measurement system or the US customary system, including the United States.
The standard state for liquids and solids is simply the state of the pure substance subjected to a total pressure of 10 5 Pa (or 1 bar). For most elements, the reference point of Δ f H ⦵ = 0 is defined for the most stable allotrope of the element, such as graphite in the case of carbon , and the β-phase ( white tin ) in the case of tin .
Isotherms of an ideal gas for different temperatures. The curved lines are rectangular hyperbolae of the form y = a/x. They represent the relationship between pressure (on the vertical axis) and volume (on the horizontal axis) for an ideal gas at different temperatures: lines that are farther away from the origin (that is, lines that are nearer to the top right-hand corner of the diagram ...
The millimeter of mercury by definition is 133.322387415 Pa [5] (13.5951 g/cm 3 × 9.80665 m/s 2 × 1 mm), which is approximated with known accuracies of density of mercury and standard gravity. The torr is defined as 1 / 760 of one standard atmosphere, while the atmosphere is defined as 101325 pascals.
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0 °C (32 °F) and standard gravity (g n = 9.806 65 m/s 2). [2] It was used as a reference condition for physical and chemical properties, and the definition of the centigrade temperature scale set 100 °C as the boiling point of water at this pressure.
Pressure in water and air. Pascal's law applies for fluids. Pascal's principle is defined as: A change in pressure at any point in an enclosed incompressible fluid at rest is transmitted equally and undiminished to all points in all directions throughout the fluid, and the force due to the pressure acts at right angles to the enclosing walls.
The CGS unit of pressure is the barye (Ba), equal to 1 dyn·cm −2, or 0.1 Pa. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre ("g/cm 2" or "kg/cm 2") and the like without properly identifying the force units. But using the names kilogram, gram, kilogram-force, or gram-force (or their symbols) as units ...