6.21   Comment on the thermodynamic stability of NO(g), given

1/2 N_2(g) + 1/2 O_2(g)\rightarrow NO(g) ; \Delta _ rH ^ \ominus = 90 kJ mol ^{-1}\\\\ .\: \: \: NO(g) + 1/2 O_2(g) \rightarrow NO_ 2(g) : \Delta _ r H^ \ominus = -74 kJ mol ^{-1}


Answers (1)
M manish

The formation of NO is unstable because \Delta _rH is positive it means heat is absorbed during the reaction. So,  NO(g) has higher energy than its reactants N_{2} and O_{2}.
On the other hand, NO_{2} is stable because \Delta _rH is negative means heat is released during the formation of NO_{2}. It is stablised with minimum energy. Hence unstable NO changes to stable NO_{2}.