We’re being asked **to determine the standard enthalpy change of formation (ΔH˚ _{f})** for

$\overline{){\mathbf{\u2206}}{\mathbf{H}}{{\mathbf{\xb0}}}_{{\mathbf{rxn}}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}{\mathbf{\u2206}}{\mathbf{H}}{{\mathbf{\xb0}}}_{\mathbf{f}\mathbf{,}\mathbf{}\mathbf{products}}{\mathbf{}}{\mathbf{-}}{\mathbf{}}{\mathbf{\u2206}}{\mathbf{H}}{{\mathbf{\xb0}}}_{\mathbf{f}\mathbf{,}\mathbf{}\mathbf{reactants}}}$

We’re given the **ΔH˚ _{rxn}** for the combustion of 2 moles of SO

2 SO_{2}(g) + O_{2}(g) → 2 SO_{3}(g) ΔH°rxn = -198 kJ

Use the ΔH°f and ΔH°rxn information provided to calculate ΔH°f for SO_{3}(g):

2 SO_{2}(g) + O_{2}(g) → 2 SO_{3}(g) ΔH°rxn = -198 kJ

ΔH°f (kJ/mol)

SO_{2}(g) -297

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