• question_answer The enthalpies of formation of ${{C}_{2}}{{H}_{2(g)}}$ and ${{C}_{6}}{{H}_{6(g)}}$at 298 K are 230 and $85\text{ }kJ\text{ }mo{{l}^{-1}}$respectively. The enthalpy change $\Delta H$ for the polymerisation of acetylene at 298 K is A)  $+205\text{ }kJ\text{ }mo{{l}^{-1}}$                 B)  $-205\text{ }kJ\text{ }mo{{l}^{-1}}$C)  $+605\text{ }kJ\text{ }mo{{l}^{-1}}$    D)  $-605\text{ }kJ\text{ }mo{{l}^{-1}}$

$3{{C}_{2}}{{H}_{2}}\xrightarrow{Polymerisation}{{C}_{6}}{{H}_{6}}$   $\Delta H$ = enthalpy of product - enthalpy of reactant $=85-3(230)$ $=85-690$ $=-605\,kJ\,mo{{l}^{-1}}$