Answer
$-305.3\ kJ/mol$
Work Step by Step
Enthalpies of formation (kJ/mol):
$CO_2(g): -393.509, H_2O(l): -285.83, CHCl_3(g): -103.1$
Methane combustion: $-890.4=-393.509+2\times-285.83-\Delta_f H_{CH_4}$ $\Delta_f H_{CH_4}=-74.7\ kJ/mol$
HCl decomposition:
$184.6=-2\times\Delta_f H_{HCl}$
$\Delta_f H_{HCl}=-92.3\ kJ/mol$
Main reaction:
$-103.1+3\times-92.3- -74.7=-305.3\ kJ/mol$
