Question

The standard enthalpies of formation of $A$ $A\left( NH _{3}\right), B\left( CO _{2}\right), C(H I)$ are respectively $-46.19,-393.4,+24,94$ and $-296.9 \,kJ\,mol ^{-1}$, The increasing order of their stability is

• A. $B < D < A < C$
• B. $C < A < D < B$
• C. $D < B < C < A$
• D. $A < C < D < B$

Answer 1

Answer: (B)

Lower the value of standard enthalpy of formation, higher the stability. The increasing order of standard enthalpies of formation of given molecules is
$ \underset{B(CO_2)}{-393.4} < \underset{D(SO_2)}{296.9}\,< \underset{A(NH_3)}{-46.19}\,< \underset{C(HI)}{24.94}\, $
Thus, the increasing order of stability is $ C < A < D < B $