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 `X-H` bond as `350kJ mol^(-1))`.
`2C_((s))+H_(2(g))rarr C_(2)H_(2(g)), Delta=225kJ mol^(-1)`
`2C_((g))rarr 2C_(g)), DeltaH=1410kJ mol^(-1)`
`H_(2(g)) rarr 2H_((g)),DeltaH=330kJ mol^(-1)`

Options

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

Answer

D

Explanation

Ethyne molecule breaks as
`C_(2)H_(2(g))rarr 2C_((g))+2H_((g)) ….(i)`
Given equations are
`2C_((s))+H_(2(g))rarr H-C-=C-H_((g)) , DeltaH=225kJ mol^(-1) ....(ii)`
`2C_((s)) rarr 2C_((g)), DeltaH=1410kJ mol^(-1) ...(iii)`
`H_(2(g))rarr 2H_((g)), DeltaH=330kJ mol^(-1) ...(iv)`
`:. 225=2xxDeltaH_(su b)C_((s))+B.E._((H_(2)))-2B.E._(C-H)-1xxB.E._(c-=C)`
`225=2xx705+330-2xx350-B.E._(C-=C)`
`225=1410+330-700-B.E._(C-=C)`
`:. B.E._(C-=C)=815kJ mol^(-1)`