4 Fe(s) + 3 O_{2}(g) → 2 Fe_{2}O_{3}(s)

We can use the following equation to solve for ΔH˚rxn:

$\overline{){\mathbf{\Delta H}}{{\mathbf{\xb0}}}_{{\mathbf{rxn}}}{\mathbf{=}}{\mathbf{\Delta H}}{{\mathbf{\xb0}}}_{\mathbf{f}\mathbf{,}\mathbf{}\mathbf{prod}}{\mathbf{-}}{\mathbf{\Delta H}}{{\mathbf{\xb0}}}_{\mathbf{f}\mathbf{,}\mathbf{}\mathbf{react}}}$

$\mathbf{\Delta H}{\mathbf{\xb0}}_{\mathbf{rxn}}\mathbf{=}\left[\mathbf{(}\mathbf{2}\mathbf{}\overline{)\mathbf{mol}\mathbf{}{\mathbf{Fe}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}}\mathbf{)}\left(\frac{\mathbf{-}\mathbf{824}\mathbf{.}\mathbf{2}\mathbf{}\mathbf{kJ}}{\mathbf{1}\mathbf{}\overline{)\mathbf{mol}\mathbf{}{\mathbf{Fe}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}}}\right)\right]\mathbf{-}\left[\mathbf{(}\mathbf{0}\mathbf{+}\mathbf{0}\right]$

Dry chemical hand warmers utilize the oxidation of iron to form iron oxide according to the following reaction:

**4 Fe(s) + 3 O _{2}(g) → 2 Fe_{2}O_{3}(s)**

**Standard thermodynamic quantities for selected substances at 25 ^{o}C **

Reactant or product | ΔH°_{f} (kJ/mol) |

Fe(s) | 0.0 |

O_{2}(g) | 0.0 |

Fe_{2}O_{3}(s) | -824.2 |

Calculate ΔH°_{rxn} for this reaction and calculate how much heat is produced from a hand warmer containing 15.0 g of iron powder.

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