What is #DeltaH_f^@# for #NO(g)#?

1 Answer
Nov 20, 2016

Answer:

For #"NO"#, #DeltaH_f""^@=+91.3*kJ*mol^-1#; and thus here #DeltaH_f""^@-=DeltaH_"rxn"^@#

Explanation:

To account for the positive value, consider what #DeltaH_f""^@# represents:

" the enthalpy associated with the formation of 1 mole of substance from its constituent elements in their standard states under given conditions....... "

So here, #DeltaH_f""^@# is the enthalpy associated with the following reaction:

#1/2N_2(g) + 1/2O_2(g) rarr NO(g)# #;DeltaH""^@""_"rxn"=91.3*kJ*mol^-1#

In order to make the #N=O# bond, we have to break exceptionally strong #N-=N# and #O=O# bonds. The energy shortfall is anticipated.