Final answer:
The thermite reaction is a highly exothermic redox reaction between aluminum and iron(III) oxide, generating molten iron and aluminum oxide, which is used for welding due to the heat produced.
Step-by-step explanation:
Thermite Reaction
The thermite reaction is a highly exothermic redox chemical reaction between aluminum metal and iron(III) oxide, which results in molten iron and aluminum oxide. This reaction is represented by the chemical equation 2 Al(s) + Fe₂O₃ (s) → 2 Fe(s) + Al₂O₃(s), and it releases a large amount of heat (>−850.2 kJ) enough to melt iron. Because of the intense heat produced, the molten iron from the reaction can be used for joining metal parts, such as in railroad track welding.
The reaction starts with a source of heat, like a Bunsen burner or a match, to initiate the process. The violent reaction that follows generates enough heat to reduce the iron oxide to iron, as the aluminum is oxidized. The reaction is so energetic that the product, iron, is in its liquid state despite iron normally melting at a high temperature of 1,536°C.
Upon cooling, the product of the thermite reaction is a lump of iron, which will have completely different physical properties than the original reactants—specifically, the reaction produces a metal that is magnetic due to the presence of iron. This iron, when cooled, forms a strong bond between surfaces, illustrating a practical application of the thermite reaction in welding.