Answer
$$CuCl_2(s) + Cu(s) \longrightarrow 2 CuCl(s)$$
$\Delta H^o_{rxn} = 82.9 \ kJ/mol$
Work Step by Step
1. Reverse the first equation:
$$CuCl_2(s) \longrightarrow Cu(s) + Cl_2(g) $$
$\Delta H^o_{rxn} = 220.1 \ kJ/mol$
2. Sum the result with the second equation:
$$CuCl_2(s) + 2 Cu(s) + Cl_2(g) \longrightarrow Cu(s) + Cl_2(g) + 2 CuCl(s)$$
Removing the ones that appear on both sides:
$$CuCl_2(s) + Cu(s) \longrightarrow 2 CuCl(s)$$
$\Delta H^o_{rxn} = 220.1 \ kJ/mol - 137.2 \ kJ/mol = 82.9 \ kJ/mol$
