question_answer 1)

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

Answer:

\[NO(g)\] 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\[N{{O}_{2}}\].