Using the data provided , calculate the multiple bond energy `(Kamal^(-1))` of a `C-= C` bond in `C_2H_2` .That energy is ( take the bond energy of a C-H bond as `350 kJ mol^(-1)) .`
`2C(s)+H_2(g)rarrC_2H_2(g)DeltaH=225 kJmol^(-1) `
`2C(s)rarr2C(g)DeltaH=1410kJmol^(-1)`
`H_2(g)rarr2H(g)DeltaH=330 kJmol^(-1)`

Options

A. 1165
B. 837
C. 865
D. 815

Answer

D

Explanation

For calculation of `C -= C` bond energy, we must first calculate dissociation energy of `C_(2)H_(2)` as
`C_(2)H_(2 )" " … (i)`
Using the given bond energies and enthalpies:
`C_2 H_2 (g) rarr 2C(s) + H_(2)(g) , Delta H = -225 kJ" "……(ii)`
`2C (s) rarr 2C(g) , " "Delta H = 1410 kJ " "....(iii)`
`H_(2) (g ) rarr 2H(g) , " "Delta H = 330 kJ" "....(iv)`
Adding Eqs. (ii),(iii) and (iv) gives Eq. (i)
`implies C_2H_2(g) rarr 2C(g) + 2H(g) , " "Delta = 1515 kJ`
`implies 1515 kJ = 2 xx (C - H) BE + (C -= C) BE = 2 xx 350 + (C -= C) BE`
`implies (C -= C) BE = 1515 - 700 = 815 kJ//mol".