4J.7) 7th edition of the textbook

[Katie Frei 1L]

In part (b) of problem 4J.7) in the 7th edition of the textbook, you have to calculate the standard reaction enthalpy of the equation 2F2(g) + 2H20(l) produces 4HF(aq) + O2(g). Why does the solutions manual only take into account the enthalpy of formation for HF and H2O when calculating the standard reaction enthalpy?

[PranitKumaran1F]

The enthalpy of formation of any element in its stable form, which in this case is F2 and O2, is always zero, so there isn't a need to take their enthalpies of formations into account.

[Amy Lefley 1J]

It makes sense that you do not include elements like F2 and O2 in the enthalpy of formation equation because these diatomic molecules are already in their most stable form so it does not take any energy to get them into their most stable form.