At $25°\mathrm{C}$ and 1 atm pressure, the enthalpy of combustion of benzene (1) and acetylene (g) are $-3268 \mathrm{kJ}{ \mathrm{mol}}^{-1}$ and $-1300 \mathrm{kJ}{ \mathrm{mol}}^{-1}$, respectively. The change in enthalpy for the reaction $3{\mathrm{C}}_2{\mathrm{H}}_2( \mathrm{g})\to {\mathrm{C}}_6{\mathrm{H}}_6\left(\mathrm{l}\right)$, is