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Chemwiki

Thermite Reaction

Chemical Concepts Demonstrated

  • Exothermicity
  • Heat capacity
  • Oxidation/reduction
  • Enthalpy/entropy

Demonstration

The crucible shown contains:
  • a Thermite mixture (3 parts by weight of Fe2O3 to 1 part powdered Al)
  • the starter (BaO2 and 400-mesh Al)
  • powdered KMnO4
The crucible is placed in a ring stand directly above the sand box.

3-5 drops of glycerin are added to the KMnO4

40-parii.gif40-part1.gif






 

Observation

The reaction occurs, melts the steel wool at the bottom of the crucible, and causes liquid iron to pour out from the resulting gap.

Explanation (including important chemical equations)

This mechanism has an unfavorable entropy.  A much more favorable enthalpy provokes and carries the reaction.  The resulting heat from the demonstration itself melts the iron product formed.  The total energy released in this experiment is equal to 851.5 kJ.

Fe2O3 + 2 Al -> 2 Fe + Al2O3

The term "Thermite" refers to the mixture of aluminum and ferric oxide used in this experiment.  It is sold commercially and is used for such applications as railroad welding and incendiary bombs.