Question

what is the overall electrochemical reaction taking place in rusting

Answer 1

Rusting is a very complicated process which involves multiple steps. Overall it is

4Fe + 3O2 →2Fe2O3

But where is water? We all know that we need water for rusting!

2Fe + O2 + 2H2O → 2Fe(OH)2

4Fe(OH)2 + O2 + 2H2O→4Fe(OH)3

2Fe(OH)3 →Fe2O3 + 3H2O

Overall:

4Fe + 2O2 + 4H2O → 4Fe(OH)2

4Fe(OH)2 + O2 + 2H2O→4Fe(OH)3

4Fe(OH)3 →2Fe2O3 + 6H2O

And

4Fe + 3O2 → 2Fe2O3