Editing Standard state (section)

=== Liquids and solids ===
The standard state for liquids and solids is simply the state of the pure substance subjected to a total pressure of {{val|e=5|u=Pa}} (or 1 [[bar (unit)|bar]]). For most elements, the reference point of Δ<sub>f</sub>''H''<sup>⦵</sup>&nbsp;= 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]]. An exception is white [[phosphorus]], the most common allotrope of phosphorus, which is defined as the standard state despite the fact that it is only [[metastability|metastable]].<ref>Housecroft C.E. and Sharpe A.G., ''Inorganic Chemistry'' (2nd ed., Pearson Prentice-Hall 2005) p.392</ref> This is because the thermodynamically stable black allotrope is difficult to prepare pure.<ref>{{cite journal |last1=Rard |first1=Joseph A. |last2=Wolery |first2=Thomas J. |date=2007 |title=The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA |url=https://link.springer.com/article/10.1007/s10953-007-9205-7 |journal=Journal of Solution Chemistry |volume=36 |issue= 11–12|pages=1585–1599 |doi=10.1007/s10953-007-9205-7 |access-date=24 December 2023 |quote=Although white phosphorus is not the thermodynamically stable allotrope, the red and black forms are difficult to prepare in pure form, which makes them less suitable for quantitative thermodynamic measurements.}}</ref>