A thermodynamic study of $\mathrm{DyCl}_3$ (E.H.P. Cordfunke, et al., J. Chem. Thermodynamics 28, 1387 (1996)) determined its standard enthalpy of formation from the following information
(1) $\mathrm{DyCl}_3(\mathrm{~s}) \rightarrow \mathrm{DyCl}_3(\mathrm{aq}$, in $4.0 \mathrm{M} \mathrm{HCl}) \quad \Delta_{\mathrm{r}} H^{\ominus}=-180.06 \mathrm{~kJ} \mathrm{~mol}^{-1}$
(2) $\mathrm{Dy}(\mathrm{s})+3 \mathrm{HCl}(\mathrm{aq}, 4.0 \mathrm{~m}) \rightarrow \mathrm{DyCl}_3(\mathrm{aq}$, in $4.0 \mathrm{M} \mathrm{HCl}(\mathrm{aq}))+\frac{3}{2} \mathrm{H}_2(\mathrm{~g})$ $\Delta_{\mathrm{r}} H^{\ominus}=-699.43 \mathrm{~kJ} \mathrm{~mol}^{-1}$
(3) $\frac{1}{2} \mathrm{H}_2(\mathrm{~g})+\frac{1}{2} \mathrm{Cl}_2(\mathrm{~g}) \rightarrow \mathrm{HCl}(\mathrm{aq}, 4.0 \mathrm{M}) \quad \Delta_{\mathrm{r}} H^{\ominus}=-158.31 \mathrm{~kJ} \mathrm{~mol}^{-1}$
Determine $\Delta_{\mathrm{f}} H^{\ominus}\left(\mathrm{DyCl}_3, \mathrm{~s}\right)$ from these data.
-994.3