For this problem, we use the Hess' Law.
ΔHrxn = ∑(ν*Hf of products) - ∑(ν*Hf of reactants)
The ν represents the corresponding stoichiometric coefficients of the substances, while Hf is the heat of formation. For pure elements, Hf = 0.
Hf of Al₂O₃ = −1676.4 kJ/mol
Hf of Fe₂O₃ = -826.0 kJ/mol
Thus,
ΔHrxn = 1*−1676.4 kJ/mol + 1*-826.0 kJ/mol
ΔHrxn = -2502.4 kJ/mol