Question

Using the data provided, calculate the multiple bond energy `(kJ mol^(-1))` of a `C-=C` bond in `C_(2)H_(2)`. That energy is `(` take the bond energy of a `C-H` bond as `350kJ mol^(-1))`.
`2C_((s))+H_(2(g))rarr C_(2)H_(2(g)), Delta=225kJ mol^(-1)`
`2C_((s))rarr 2C_(g)), DeltaH=1410kJ mol^(-1)`
`H_(2(g)) rarr 2H_((g)),DeltaH=330kJ mol^(-1)`
A. `1165`
B. `837`
C. `865`
D. `815`

Answer 1

Correct Answer - D
Desired equation is
`H-C-=C-Hto2C(g)+2H(g)DeltaH=?` ……..`(i)`
Given equations are
`2C(g)+H_(2)(g)toC_(2)H_(2)(g)` …….`(ii)` `DeltaH=225 kJ//mol`
`2C(s)to2C(g)`, `DeltaH=1410 kJ//mol`…`(iii)`
`H_(2)(g)to2H(g)`, `DeltaH=330 kJ//mol`.......`(iv)`
By adding eqn `(iii)` and `(iv)` and then subtracting eq. `(i)`
`:. H-C-=CHto2C(g)+2H(g)`
`DeltaH=1410+330225=1515 kJ//mol`.
Reaction `(i)` involves the breaking of `2C-H` bonds and one `C-=C` bond
or `1515 kJ//mol=(2xx350)kJ+C-=C` bond
`=(1515-700)kJ-=815kJ//mol`