# What is reduction?

Dec 6, 2014

Redox reactions involve the transfer of electrons (${e}^{-}$)from one compound to another. These reactions differ from acid-base reactions because we are no longer dealing with protons (${H}^{+}$), but instead with electrons.

The substance that lost electrons (the substance that was oxidized) is called a reducing agent, while the substance that gained electrons (the substance that was reduced) is called an oxidation agent.

We use oxidation numbers to keep track of the electrons transferred in a redox reaction. The rules for assigning oxidation numbers to each atom belonging to a compound involved in a redox reaction are pretty straightforward, as you can see here

http://www.occc.edu/kmbailey/chem1115tutorials/oxidation_numbers.htm

Therefore, a reduction is a chemical reaction in which a compound gains electrons. Here's an example to better illustrate this:

$C {H}_{4} + 2 {O}_{2} \to C {O}_{2} + 2 {H}_{2} O$

Let's assign oxidation numbers (ON) for every atom (I will not go into the rules for doing this here)

${C}^{- 4} {H}_{4}^{+ 1} + 2 {O}_{2}^{0} \to {C}^{+ 4} {O}_{2}^{- 2} + 2 {H}_{2}^{+ 1} {O}^{- 2}$

As you can see, $C$ went from ON = $- 4$ on the reactsnts' side, to ON = $+ 4$ on the products' side - it LOST $8 {e}^{-}$

$O$, on the other hand, went from ON = $0$ on the reactsnts' side, to ON = $- 8$ on the products' side - it GAINED $8 {e}^{-}$.

Therefore, the oxygen was reduced by the carbon, while the carbon was oxidized by the oxygen.