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Question

# The thermite process is used for welding railway track together. In this reaction, aluminum reduces iron(III) oxide to metallic iron:$2 AI(s) + Fe2O3(s)→2 Fe(s) + Al2O3(s)$Igniting a small charge of barium peroxide mixed with aluminum triggers the reaction of a mixture of aluminum powder and iron (III) oxide; the molten iron produced flows into the space between the steel rails that are to bejoined. (a) Calculate the standard enthalpy change ΔH° for this reaction, using data from Appendix D. (b) Calculate the heat given off when 3.21 g iron(III) oxide is reduced by aluminum at constant pressure.

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a) $\Delta H^{\circ}=\{(2 \mathrm{mol}) \Delta H_{f}^{o}[\mathrm{Fe}(s)]+(1 \mathrm{mol}) \Delta H_{\mathrm{f}}^{e}[\mathrm{Al}_{2} \mathrm{O}_{3}(s)]\}$

$-\{(2 \mathrm{mol}) \Delta H_{\mathrm{f}}^{\circ}[\mathrm{Al}(s)]+(1 \mathrm{mol}) \Delta H_{\mathrm{f}}^{e}[\mathrm{Fe}_{2} \mathrm{O}_{3}(s)]\}$

$=(2 \mathrm{mol}) \times 0+(1 \mathrm{mol})\times(-1675.7 \mathrm{kJ} \mathrm{mol}^{-1})$

$-\{(2 \mathrm{mol}) \times 0+(1 \mathrm{mol})\times(-824.2 \mathrm{kJ} \mathrm{mol}^{-1})\}$

$=-1675.7 \mathrm{kJ}+824.2 \mathrm{kJ}$

$=-851.5 \mathrm{kJ}$

The enthalpy change $\Delta H^{\circ}=n \Delta H_{\mathrm{f}}^{o}( Products )-n \Delta H_{\mathrm{f}}^{\circ}(Reactants )$

$2 \mathrm{Al}(s)+\mathrm{Fe}_{2} \mathrm{O}_{3}(s) \rightarrow 2 \mathrm{Fe}(s)+\mathrm{Al}_{2} \mathrm{O}_{3}(s)$

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