 
       
      
    6.21. Comment on the thermodynamic stability of NO (g), given
 
 
                
                  The formation of  is unstable because 
 is positive, which means heat is absorbed during the reaction. So, 
(g) has higher energy than its reactants 
 and 
.
On the other hand,  is stable because 
 is negative, which means heat is released during the formation of 
. It is stabilised with minimum energy. Hence, unstable 
 changes to stable 
.
 
                 
                