Question

What is reduction?

Answer 1

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:

`CH_4 + 2O_2 -> CO_2 + 2H_2O`

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) + 2O_2^0 -> C^(+4)O_2^(-2) + 2H_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 `8e^(-)`.

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