• # question_answer 34) Comment on the thermodynamic stability of NO(g), given $\frac{1}{2}N(g)+\frac{1}{2}{{O}_{2}}(g)\to NO(g)$ ${{\Delta }_{r}}{{H}^{{}^\circ }}=90kJ\,mo{{l}^{-1}}$ $NO(g)+\frac{1}{2}{{O}_{2}}(g)\to N{{O}_{2}}(g)$ ${{\Delta }_{r}}{{H}^{{}^\circ }}=-74kJ\,mo{{l}^{-1}}$

$NO(g)$ is less stable than $N{{O}_{2}}$ because $NO$is endothermic compound whereas $N{{O}_{2}}$ is exothermic compound. Exothermic compounds are always more stable than endothermic compounds. Thus, in second step, $NO$ changes to more stable$N{{O}_{2}}$.