My question is somewhat related to this question. When I look at a table of standard values there are two entries for Hydrogen:
- $\ce {H2(g)} $ - 0 kJ/mol
- $\ce {H(g)} $ - 218 kJ/mol
I understand the $\ce{H2(g)} $ is 0 because it is used as a reference, why is monatomic $\ce{ H(g)}$ given in the table and what does it mean? When would one use it in a calculation of enthalpy change?
From what I understand Hydrogen only exists as a monatomic gas at very high temperatures, the Standard enthalpies of formation are given at 1 bar, 298.15 K.