If the heats of formation of `C_(2)H_(2)` and `C_(6)H_(6)` are `230 kJ mol^(-1)` and `85 kJ mol^(-1)` respectively, the `DeltaH` value for the trimerisation of `C_(2)H_(2)` is

Options

A. `-205" kJ/mol"`
B. `+305" kJ/mol"`
C. `-605" kJ/mol"`
D. `+605" kJ/mol"`

Answer

C

Explanation

`3C_(2)H_(2(g))rarrC_(6)H_(6(g)), " "Delta H=?`
`Delta H=Sigma H_(P)-Sigma H_(R)`
`=H_(C_(6)H_(6(g)))-3xxH_(C_(2))H_(2(g)))`
`=85-3xx230=85-660=-605 kJ`.