Answer
$-2253.9\ kJ/mol$
Work Step by Step
$\begin{matrix}
Reaction&\Delta H(kJ/mol)&\times\\
\hline
Ca(s)\rightarrow Ca(g)&+178.2 &1\\
Ca(g)\rightarrow Ca^+(g)+e^-&+589.83&1\\
Ca^+(g)\rightarrow Ca^{2+}(g)+e^-&+1145.45&1\\
1/2Cl_2(g)\rightarrow Cl(g)&+121.3 &2\\
Cl(g)+e^-\rightarrow Cl^-(g)& -349 &2\\
Ca^{2+}(g)+2\ Cl^-(g)\rightarrow CaCl_2(s)&x&1\\
\hline
Ca(s)+Cl_2(g)\rightarrow CaCl_2(s)&-795.8&
\end{matrix}$
Solving for x we get: $-2253.9\ kJ/mol$
