The bond dissociation energy of a diatomic molecule is also called bond energy. However, the bond dissociation energy depends upon the nature of bond and also the molecule in which the bond is present. The bond energy N-H bind in `NH_(3)` is equal to one-third of the energy of dissociation of `NH_(3)` because there are three N-H bonds and those of C-H bond in `CH_(4)` is equal to one-fourth of the energy of dissociation of `CH_(4)` Heat of a reaction = Bond energy of reactants - Bond energy of products
Find the bond enthalpy of S-S bond from the following data.
`C_(2)H_(5)-S-C_(2)H_(5)(g) " " Delta H_(f)^(@) = -147.23 kJ mol^(-1)`
`C_(2)H_(5)-S-S-C_(2)H_(5)(g) " " Delta H_(f)^(@) = -201.92 kJ mol^(-1)`
`S(g) Delta H_(f)^(@) = 222.80 kJmol^(-1)`

Options

A. `-277.49 kJ mol^(-1)`
B. `277.49 kJ mol^(-1)`
C. `-349.15 kJ mol^(-1)`
D. `349.15 kJ mol^(-1)`

Answer

B

Explanation

BE(S-S), `Delta H_(vap)(s)-{Delta H_(f)^(@)(C_(2)H_(5)S-SC_(2)H_(5))}`
`= Delta H_(vap)(s) - Delta H_(f)^(@) = -Delta H_(f)^(@)(C_(2)H_(5)-S-C_(2)H_(5))`
`= 222.80-{-201.92 - (- 147.23)} = 277.49 kJ mol^(-1)`