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why is white phosphorous given to have ZERO standard heat of formation??

while it is well known fact that white phosphorous is highly reactive and is obviously less stable than red and black phosphorous

also here=Which allotrope of phosphorus is kinetically the most stable?

it says that black phosphorous is thermodynamically more stable

also what is the relative stability of the allotropes [black red white purple]

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    $\begingroup$ Why do we measure height above sea level and not height below Mount Everest? $\endgroup$
    – orthocresol
    Apr 27 '19 at 17:01
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    $\begingroup$ @orthocresol cause the sea surrounds the world around and Mount Everest is only a single entity which is subject to change $\endgroup$ Apr 27 '19 at 17:03
  • $\begingroup$ All elements have one defined standard thermodynamic state. If the pure element has multiple allotropes the choice is somewhat arbitrary. For instance diamond has a more consistently defined structure than graphite, but diamonds are expensive to burn in a bomb calorimeter. So graphite is consistent enough from sample to sample, it is stable, and it is cheap. Hence the chosen standard state of carbon is graphite. $\endgroup$
    – MaxW
    Apr 27 '19 at 17:20
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    $\begingroup$ Related: chemistry.stackexchange.com/questions/73951/… $\endgroup$ Apr 27 '19 at 17:35