Question

Water is decomposed by electrolysis to form the gaseous products hydrogen, `H_2`, and oxygen, `O_2`. How do you write the balanced equation for this reaction?

Answer 1

`2"H"_2"O" -> 2"H"_2 + "O"_2`

Explanation:

One molecule of water `"H"_2"O"` can give 2 Hydrogen and 1 Oxygen atom, which is sufficient to make 1 `"H"_2` molecule and `1/2` of a molecule of `"O"_2`. You can write it as

`"H"_2"O" -> "H"_2 + 1/2"O"_2`

However, there is no such thing as half a molecule. To avoid fractions, multiply everywhere by 2. So it becomes

`2"H"_2"O" -> 2"H"_2 + "O"_2`

This means that you can make 2 molecules of `"H"_2` and 1 molecule of `"O"_2` with 2 molecules of `"H"_2"O"`.