Chapter 8.8, Problem 8.12P

The industrial degreasing solvent methylene chloride, CH₂Cl₂, is prepared from methane by reaction with chlorine:

${\text{CH}}_4(g)+2{\text{Cl}}_{\text{2}}(g)\stackrel{}{\to } {\text{CH}}_2{\text{Cl}}_2(g)+2\text{HCl}(g)$

Use the following data to calculate ΔH° in kilojoules for the reaction:

$\begin{array}{ll}{\text{CH}}_4(g)+{\text{Cl}}_2(g)\stackrel{}{\to }{\text{CH}}_3\text{Cl}(g)+\text{HCl}(g)\hfill & \Delta H°=-98.3\text{kJ}\hfill \\ {\text{CH}}_3\text{Cl}(g)+{\text{Cl}}_2(g)\stackrel{}{\to }{\text{CH}}_2{\text{Cl}}_2(g)+\text{HCl}(g)\hfill & \Delta H°=-104\text{kJ}\hfill \end{array}$