Chapter 4 - Energy and Chemical Reactions - Questions for Review and Thought - Topical Questions - Page 189e: 81b

$-595.2\,kJ/mol$

$\Delta H^{\circ}=\Sigma n_{p}\Delta H_{f}^{\circ}(products)-\Sigma n_{r}\Delta H_{f}^{\circ}(reactants)$ $=[2\Delta H_{f}^{\circ}(HF,g)+\Delta H_{f}^{\circ}(I_{2},s)]-[2\Delta H_{f}^{\circ}(HI,g)+\Delta H_{f}^{\circ}(F_{2},g)]$ $=[2(-271.1\,kJ/mol)+(0\,kJ/mol)]-[2(26.48\,kJ/mol)+(0\,kJ/mol)]$ $=-595.2\,kJ/mol$