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Encyclopedia > Standard state
The plimsoll symbol as used in shipping
The plimsoll symbol as used in shipping

In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals exactly). This pressure was changed from 1 atm (101.325 kilopascals) by IUPAC in 1990.[1] The standard state of a material can be defined at any given temperature, most commonly 25 degrees Celsius, although quite a few texts (especially in related disciplines such as physics and engineering) use 0 degrees Celsius for Standard Temperature and Pressure (STP). Image File history File links Plimsoll_line. ... Image File history File links Plimsoll_line. ... Waterline refers to an imaginary line marking the level at which ship or boat floats in the water. ... For other uses, see Chemistry (disambiguation). ... In physics, the term state is used in several related senses, each of which expresses something about the way a physical system is. ... The bar (symbol bar), decibar (symbol dbar) and the millibar (symbol mbar, also mb) are units of pressure. ... The pascal (symbol Pa) is the SI unit of pressure. ... Standard atmosphere (symbol: atm) is a unit of pressure. ... IUPAC logo The International Union of Pure and Applied Chemistry (IUPAC) (Pronounced as eye-you-pack) is an international non-governmental organization established in 1919 devoted to the advancement of chemistry. ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ... In chemistry and other sciences, STP or standard temperature and pressure is a standard set of conditions for experimental measurements, to enable comparisons to be made between sets of data. ...


It should be noted that the standard state is an arbitrarily chosen non-zero value, not a natural zero point. Choices and actions are considered to be arbitrary when they are done not by means of any underlying principle or logic, but by whim or some decidedly illogical formula. ...


For a given material or substance, the standard state is the reference state for the material's thermodynamic state properties such as enthalpy, entropy, Gibbs free energy, and for many other material standards. The standard enthalpy of formation for an element in its standard state is 0. Water and steam are two different forms of the same chemical substance A chemical substance is any material with a definite chemical composition, no matter where it comes from. ... t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ... For a less technical and generally accessible introduction to the topic, see Introduction to entropy. ... In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature and pressure. ... The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 atmosphere...


When the standard state is referred to in a chemical reaction, it also includes the condition that the concentrations of all solutions are at unity (or another designated quantity) for whatever measure of concentration is specified. If that is molarity that would be 1 mol·dm-3 and for molality 1 mol·kg-1. If mole fraction is used, the pure liquid or solid is the standard state (x=1). As it is possible (and in principle legitimate) to take a different unit for each of the species in the reaction, the nature of the standard state needs to be specified when reporting or tabulating. Although a definition involving 1 mol/L (molarity at unity) of A in combination with pure B (mole fraction at unity) is clearly a condition that can never be met, such a non-existent standard state nevertheless leads to a consistent system of tabulated values, provided it is used consistently by all. Of course these values are different from those where a different standard state is adopted. For other uses, see Chemical reaction (disambiguation). ... For other uses, see Concentration (disambiguation). ... Making a saline water solution by dissolving table salt (NaCl) in water This article is about chemical solutions. ... This page refers to concentration in the chemical sense. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... A decimetre is a measurement of length, measuring 10 centimetres or one-tenth of a metre millimetre << centimetre << decimetre << metre << kilometre ... This page refers to concentration in the chemical sense. ... “Kg” redirects here. ... The mole fraction is one way of expressing the relative concentration of a given species. ...


In the time of their development (the 19th century) the Plimsoll - symbol was adopted as a superscript o to indicate the non-zero nature of the chosen reference state. For typographic reasons this symbol is often abridged to a rather misleading zero superscript 0 in later texts. Plimsoll is the plimsoll line = plimsoll mark on as ships hull the family name of Samuel Plimsoll, the man it is named after, and of other persons, as Sir James Plimsoll, a governor of Tasmania and the fictional character Oliver Plimsoles in The League of Gentlemen (comedy) a type...


See also

In chemistry and other sciences, STP or standard temperature and pressure is a standard set of conditions for experimental measurements, to enable comparisons to be made between sets of data. ...

External links

  • IUPAC definition of standard state
  • Standard-state enthalpies

Notes

  1. ^ http://www.iupac.org/goldbook/S05910.pdf

 
 

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