Half Equations and the Thermite Process for Welding Railway Tracks

[rosie_burk]

The thermite process can be used to weld lengths of railway track together. A mould placed over the ends of the rails to be joined is filled with a charge of aluminium powder and iron(iii) oxide. When the mixture is ignited, a redox reaction occurs to form molten iron, which joins the rails together.

a. Write a half equation for the conversion of iron(iii) oxide to metallic iron.

i got Fe2O3 + 6H+ +6e- = 2Fe + 3H20- but that's wrong according to the book, the answer is Fe2O3(s) + 6e- --> 2Fe(l) + 3O 2- (s). I don't understand why they balanced it using oxygen instead of water.

b. Write the overall equation for the thermite process.

 

[chemisttree]

The thermite process can be used to weld lengths of railway track together. A mould placed over the ends of the rails to be joined is filled with a charge of aluminium powder and iron(iii) oxide. When the mixture is ignited, a redox reaction occurs to form molten iron, which joins the rails together.

a. Write a half equation for the conversion of iron(iii) oxide to metallic iron.

i got Fe2O3 + 6H+ +6e- = 2Fe + 3H20- but that's wrong according to the book, the answer is Fe2O3(s) + 6e- --> 2Fe(l) + 3O 2- (s). I don't understand why they balanced it using oxygen instead of water.

Because that would be two half reactions...

6H+ + 3O-2 ------> 3H2O

and

Fe2O3 + 6e- -------------> 2Fe(0) + 3O-2