Question

The thermite reaction, in which powdered aluminum reacts with iron oxide, is highly exothermic: 2Al(s) + F e2O3 (s)→A l2O 3 (s) + 2Fe(s) Use standard enthalpies of formation to find ΔH ∘ rxn for the thermite reaction.

Answer 1

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