`N_(2)(g)+3H_(2)(g)to2NH_(3)(g),Delta_(r)H^(0)=-92.4kJ*mol^(-1)`
What is the standard enthalpy of formation of `NH_(3)` ?

Explanation

`N_(2)(g)+3H_(2)(g)to2NH_(3)(g),Delta_(r)H^(0)=-92.4kJ`
`(1)/(2)N_(2)(g)+(3)/(2)H_(2)(g)toNH_(3)(g),Delta_(r)H^(0)=-46.2kJ` . . [1]
Equation [1] represents the formation of `NH_(3)(g)` from the constituent elements. So, the standard enthalpy change for the reaction represented by equation [1]=the standard enthalpy of formation for `NH_(3)(g)=-46.2 kJ*mol^(-1)`