# How do you define oxidation and reduction?

Jul 9, 2016

Well, you could have two variations that I can think of, and each variation can have two different wordings, I suppose...

One (general) definition and its variation is:

• When an element's oxidation state becomes more positive.
• When an element's oxidation state becomes less negative.

Example:

${\text{Fe"^(2+) -> "Fe}}^{3 +} + {e}^{-}$

Here, the half-reaction demonstrates the oxidation state of $\text{Fe}$ becoming more positive by $+ 1$.

And the other (organic) definition and its variation (that I can think of) is:

• When a species gains an oxygen.
• When a species loses a hydrogen.

Example:

${\text{Mn"^(2+) + 2"H"_2"O" -> "MnO"_2 + 4"H}}^{+} + 2 {e}^{-}$

Here, $\text{Mn}$ changes oxidation state from $+ 2$ to $+ 4$, but does so by gaining two oxygens.

You can imagine how to define reduction, the exact opposite of all of these.