The thermite reaction

CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry

Problem

The thermite reaction, used for welding railway tracks, is represented by Fe2_2O3_3(s) + 2 Al(s) → Al2_2O3_3(s) + 2 Fe(l). At 25 ∘C25\,^{\circ}\text{C} the reaction enthalpy is ΔH=−851.5 kJ mol−1\Delta H = -851.5\,\text{kJ\,mol}^{-1} and the entropy change is ΔS=−596 J mol−1 K−1\Delta S = -596\,\text{J\,mol}^{-1}\,\text{K}^{-1}. Assume these quantities remain constant with temperature. (a) Determine ΔG\Delta G for the reaction at 298 K298\,\text{K}. Report the value with units. (b) Is the thermite reaction thermodynamically favorable at room temperature? Support your answer using the value from part (a). (c) Calculate the maximum temperature (to the nearest whole kelvin) at which the reaction remains thermodynamically favorable under standard-state conditions. (d) Molten iron is produced in this reaction. Considering your result from part (c), explain why the reaction nevertheless proceeds rapidly once initiated by a high-temperature ignition source.

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