[单选题]
Given the enthalpy ch8zs8rdd: v;o- l7qccw anges for*7o(u0a - e1bp/zlhh5acp h.s,g l yud the reactions 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)?