In which of the following reactions does `DeltaH^(0)` at `25^(@)C` indicate the standard enthalpy of formation `(DeltaH_(f)^(0))` of the compound formed in each of the reactions?
(2) `N_(2)(g)+3H_(2)(g)to2NH_(3)(g)`
(2) `(1)/(2)N_(2)(g)+(1)/(3)O_(3)(g)toNO(g)`.

Explanation

(1) Here, 2 mol of `NH_(3)(g)` is produced from the stable constituent elements, `H_(2)(g) and N_(2)(g)`. Hence according to the definition, at `25^(@)C` the standard reaction enthalpy of this reaction is not equal to the standard enthalpy of formation of `NH_(3)(g)`.
(2) The standard state of oxygen at `25^(@)C` is `O_(2)(g)`. so, the given equation does not represent the formation reaction of NO(g). Consequently, at `25^(@)C` the standard reaction enthalpy of this reaction is not equal to the standard enthalpy of formation of NO(g).