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Which substances have the most extreme enthalpies of formation per gram at standard temperature and pressure?

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  • Beryllium oxide −23.96 kJ/g
  • Lithium fluoride −23.75 kJ/g
  • Beryllium fluoride −21.84 kJ/g
  • Beryllium hydroxide −21.01 kJ/g
  • Lithium hydroxide −20.24 kJ/g
  • Lithium oxide −19.93 kJ/g
  • Boron trioxide −18.29 kJ/g
  • Magnesium fluoride −18.04 kJ/g
  • Aluminum fluoride −17.98 kJ/g
  • Boron trifluoride −16.76 kJ/g
  • Aluminum oxide −16.43 kJ/g
  • Water −15.86 kJ/g
  • Magnesium hydroxide −15.85 kJ/g
  • Magnesium oxide −14.92 kJ/g
  • Hydrogen fluoride −13.66 kJ/g
  • Lithium hydride −11.4 kJ/g
  • Boron nitride −10.24 kJ/g
  • Carbon dioxide −8.941 kJ/g
  • Lithium nitride −4.73 kJ/g
  • Methane −4.6 kJ/g
  • Ammonia −2.71 kJ/g
  • Diborane 1.31 kJ/g
  • Cyclopropene 1.33 kJ/g
  • Cubane 5.73 kJ/g
  • Dicyanoacetylene 6.579 kJ/g
  • Various unstable nitrogen allotropes >10 kJ/g
  • Free hydrogen (not bound in diatomic molecules) 216.34 kJ/g
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    $\begingroup$ This is interesting, but if the answer is nothing but a list of values, sources are rather important. $\endgroup$ – Nicolau Saker Neto Apr 13 at 3:38
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    $\begingroup$ I calculated all these using data from either wikipedia or webbook.nist.gov $\endgroup$ – Jonathan Ray Apr 13 at 4:40
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Jonathan Ray has indicated he has used data from either Wikipedia or NIST Webbook in his comment. Actually, NIST Webbook is an excellent choice because it has listed wide variety of thermochemical data. However, there were few important references and points he did not mention. For example, in that tabulated data set, the state of compound(s) wasn't clear. If you look at the data reported for calcium fluoride (as liquid and solid), you may understand my point (see below table). I'm here trying to correct those facts and some other errors in above table given by my colleague. One such erroneous data is the value given for cyclopropene (g). Actually, value given above is more closed to that of cyclopropane than for cyclopropene (see below table). For readers' benefits, I also want to emphasize that Ref.1 has tabulated a lot of data, which are NIST Webbook incorporated (in case if you don't trust NIST Webbook).

$$ \begin{array}{ccc} \hline \text{Compound} &\text{Formula} & M\text{, g/mol} & \Delta_\mathrm fH^\circ\text{, kJ/mol} & \Delta_\mathrm fH^\circ\text{, kJ/g} & \text{Ref.} \\\hline \text{Beryllium oxide (s)} & \ce{BeO} & \pu{25.01} & \pu{−609.43} & \pu{-24.57} & \pu{1} \\ \beta\!-\!\text{Beryllium hydroxide (aq)} & \ce{Be(OH)2} & \pu{43.03} & \pu{−905.84} & \pu{-21.05} & \pu{2} \\ \alpha\!-\!\text{Beryllium hydroxide (aq)} & \ce{Be(OH)2} & \pu{43.03} & \pu{−902.70} & \pu{-20.98} & \pu{2} \\ \text{Lithium Hydroxide (s)} & \ce{LiOH} & \pu{23.95} & \pu{-484.93} & \pu{-20.25} & \pu{1} \\ \alpha\!-\!\text{Aluminium oxide (s)} & \ce{Al2O3} & \pu{101.96} & \pu{-1675.69} & \pu{-16.43} & \pu{1,3}\\ \text{Calcium fluoride (s)} & \ce{CaF2} & \pu{78.07} & \pu{-1225.91} & \pu{-15.70} & \pu{1} \\ \text{Calcium fluoride (l)} & \ce{CaF2} & \pu{78.07} & \pu{-1186.07} & \pu{-15.19} & \pu{1} \\ \text{Hydrogen fluoride (g)} & \ce{HF} & \pu{20.01} & \pu{-272.55} & \pu{-13.62} & \pu{1} \\ \text{Cyclopropane (g)} & \ce{C3H6} & \pu{42.08} & \pu{53.30} & \pu{1.27} & \pu{4}\\ \text{Nitric oxide (g)} & \ce{NO} & \pu{30.01} & \pu{90.29} & \pu{3.01} & \pu{1}\\ \text{Cubane (g)} & \ce{C8H8} & \pu{104.15} & \pu{622.2} & \pu{5.97} & \pu{5}\\ \text{Cubane (g)} & \ce{C8H8} & \pu{104.15} & \pu{597.1} & \pu{5.73} & \pu{6}\\ \text{Cyclopropene (g)} & \ce{C3H4} & \pu{40.06} & \pu{277} & \pu{6.91} & \pu{7}\\ \text{2-Butynedinitrile (g)} & \ce{NCCCCN} & \pu{76.06} & \pu{533.46} & \pu{7.01} & \pu{1}\\ \text{Acetylene (g)} & \ce{HCCH} & \pu{26.04} & \pu{226.73} & \pu{8.71} & \pu{1}\\ \hline \end{array} $$

References:

  1. M. W. Chase, Jr., NIST-JANAF Themochemical Tables, Fourth Edition, J. Phys. Chem. Ref. Data, Monograph 9, 1998, 1–1951.
  2. I. J. Bear, A. G. Turnbull, “The Heats of Formation of Beryllium Compounds. I. Beryllium Hydroxides,” J. Phys. Chem. 1965, 69(9), 2828–2833 (DOI: 10.1021/j100893a004).
  3. R. C. King, G. T. Armstrong, “Heat of Combustion and Heat of Formation of Aluminum Carbide,” Journal of Research of the National Bureau of Standards–A. Physics and Chemistry 1964, 68A(6), 661–668 (http://dx.doi.org/10.6028/jres.068A.066).
  4. J. W. Knowlton, F. D. Rossini, “Heats of combustion and formation of cyclopropane,” Journal of Research of the National Bureau of Standards 1949, 43(2), 113–115 (http://dx.doi.org/10.6028/jres.043.013).
  5. B. D. Kybett, S. Carroll, P. Natalis, D. W. Bonnell, J. L. Margrave, J. L. Franklin, “Thermodynamic Properties of Cubane,” J. Am. Chem. Soc. 1966, 88(3), 626–626 (DOI: 10.1021/ja00955a056).
  6. A. Bashir-Hashemi, J. S. Chickos, W. Hanshaw, H. Zhao, B. S. Farivar, J. F. Liebman, “The enthalpy of sublimation of cubane,” Thermochimica Acta 2004, 424(1-2), 91–97 (https://doi.org/10.1016/j.tca.2004.05.022).
  7. K. B. Wiberg, W. J. Bartley, F. P. Lossing, “On the strain energy in cyclopropene and the heat of formation of the $\ce{C3H4+}$ ion,” J. Am. Chem. Soc. 1962, 84(20), 3980–3981 (DOI: 10.1021/ja00879a049).
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