Dry chemical hand warmers utilize the oxidation of iron to form iron oxide according to the following reaction: 4Fe (s) + 3O2 (g) →2Fe2O3 (s) Standard thermodynamic quantities for selected substances at 25 ∘C Reactant or product ΔH∘f (kJ/mol) Fe (s) 0.0 O2 (g) 0.0 Fe2O3 (s) - 824.2 Calculate ΔH∘rxn for this reaction.

-1648.4 kJ/mol

Explanation:

Based on Hess's law:

ΔHr = ∑n*ΔH°f (products) - ∑n*ΔH°f (reactants)

In the reaction:

4Fe (s) + 3O₂ (g) → 2Fe₂O₃ (s)

ΔHr = 2 ΔH°f {Fe₂O₃} - (4ΔH°f {Fe (s) } + 3ΔH°f{O₂ (g) }

As:

ΔH°f {Fe₂O₃} = - 824.2kJ/mol

ΔH°f {Fe (s) } = 0.0kJ/mol

ΔH°f{O₂ (g) } = 0.0kJ/mol.

Thus,

ΔHr = 2 ₓ - 824.2kJ/mol =

-1648.4 kJ/mol