The reaction in which hydrogen and oxygen are produced by running an electric current through water is an example of

The answer is electrolysis. This is the chemical reaction that decomposes a substance (usually while in its liquid state) to its components by passing an electric current through it. Electrolysis of water is used to produce hydrogen fuel and also produce oxygen that can be used to supplement breathable air such as in submarines.

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !