The bond energy of NO is 632 kl/mol and that of each N-O bond in N02 is 469kj/mol. Using lewis structures and and the average bond energies explain the difference between the two molecules and the fact that the bond energies of the two bonds in NO2 are the same.
The Lewis structure for NO and NO2 show that thebond order in NO is a double bond and that in NO2 is 1.5 on average. . . . : N=O : - NO
. .. . : O - N = O : - NO2 . .
Bond enthalpy of NO at 632 kJ∙mol-1 is close to N=O value listed in table, whereas the N-O bond enthalpy in NO2 is of 469 kJ∙mol-1 is slightly greater than the average of a N-O single and N=O double bond; ½ (630 kJ + 210 kJ) = 420 kJ.