4.4.13 Thermit® Reaction

1.Experimental setup 2.Combustion of the ignition mixture
Experimental setup Combustion of the ignition mixture
3.Thermit reaction begins; white hot liquid iron seeps out 4.Reaction product: elemental iron
Thermit® reaction begins; white hot liquid iron seeps out Reaction product: elemental iron
Animation of Experiment (GIF Format, 428k)
Animation of Experiment (MPG Format, 368k)

Photo 1:Experimental setup: A flowerpot with a single drainage hole is filled with a mixture of iron oxide (Fe2O3) and coarsely ground aluminum (reaction mixture: Thermit® mixture). This is covered with a mixture of magnesium and barium peroxide (BaO2) (ignition mixture). A strip of magnesium serves as a wick. A porcelain dish filled with sand is placed underneath.

Photo 2:The magnesium-barium peroxide mixture is ignited by the burning magnesium ribbon. Magnesium oxide and barium oxide are produced in a strongly exothermic reaction according to:

BaO2 + Mg        > BaO + MgO
The heat emitted by this reaction ignites the Thermit® mixture.

Photos 3, 4:Due to very high temperatures (up to 2400C, reaction enthalpy: 852 kJ/mol) the reation of iron oxide with aluminum forms elemental iron, which seeps in liquid form out of the flower pot drainage hole:

Fe2O3 + 2 Al        > 2 Fe + Al2O3
The molten iron is collected in the porcelain dish where it immediately hardens. An afterglow can be clearly seen.

The Thermit® process is used to weld and join iron parts (such as iron tracks and street car tracks). A number of other metals can be obtained from their oxides by reduction with aluminum.

Exercise 4.4.13.1:
Solution:
The amount of heat energy released during a Thermit reaction is determined to be -661.1 kJ. Given a surplus of iron oxide, how many grams of alumninum were used during the reaction?
Exercise 4.4.13.2:
Solution:
How many grams of aluminum are necessary to raise the temperature of 200 g water from 20 C to 80 C?

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