[单选题]
Given the enthalpy changes for the rearvgw15z :gf uw2v +r.o0q9fhy ction:njk bno5fn f/i )up/;e* gtuk12n (uqs below.
$\frac{1}{2}$$N_2$(g)+$O_2$(g)→$NO_2$(g); ΔH=+33.9kJ
$NO$(g)+$\frac{1}{2}$$O_2$(g)→$NO_2$(g); ΔH=-56.5kJ
What will be the enthalpy change for:
$\frac{1}{2}$$N_2$(g)+$\frac{1}{2}$$O_2$(g)→$NO$(g)?