Why is the Gibbs free energy of formation for oxygen (O2) 231.7 kJ/mol according to WolframAlpha?

Prior to stumbling upon this measurement in WolframAlpha, I was under the impression that all elements (including diatomic elements) have a free energy of formation of zero. I checked it for N2 and it returned 0 kJ/mol. Is this a mistake or am I missing something?

1 Answer
Truong-Son N.
Apr 25, 2018

Because Wolfram Alpha is wrong. That is the #Delta_fG^@# for #"O"(g)#, and not #"O"_2(g)#. Search for #"231.7"# on here, and you'll find that #Delta_fG^@# for #"O"_2(g)# is indeed zero. Note that if you cite data from this page, you should go find the value from the JANAF tables or NIST, which are where the values came from.

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