Oxidation-reduction reactions

The few simple reactions considered so far all involve oxidation, or its opposite, reduction. Such reactions are among the most important in chemistry. Many processes that take place

Dinitrogen pentoxide N_PO_s W 9 lit w +5

Nitrogen dioxide N0₂ tt^^^^® +⁴

— - H -

Dinitrogen trioxide N₂0₃ Q-^-Q-^-Q +3

Nitric oxide NO n_____ r*\ +2

-\ 1

Nitrous oxide N₂0

Nitrogen N₂

Hydroxylamine NH₂OH

Hydrazine

Ammonia

in living organisms, for example, depend on a whole series of interdependent oxidation-re­duction reactions.

Despite its name, an oxidation reaction does not necessarily involve oxygen atoms. However, all reactions in which oxygen is added to an element or compound are consid­ered oxidation reactions. Similarly, whenever oxygen is removed from a compound, such a reaction is also always known as a reduction reaction. The chemical definition of an oxida­tion reaction is one in which the " oxidation state" or " oxidation number" of an atom in­creases. This means that the formal electric charge on the atom becomes more positive. Similarly, a reduction reaction is one in which the oxidation state decreases. The formal elec­tric charge in this case becomes more nega­tive. All atoms in their neutral states are always considered to have an oxidation state equal to zero.

For example, water can be formed from hy­drogen and oxygen gases. During the reaction of these gases, the hydrogen atoms move from an oxidation state of zero to one of +1. They are said to have been oxidized. Con­versely, the oxidation state of the oxygen atoms goes from zero to —2. They have been reduced. The formation of water thus involves simultaneously a reduction and an oxidation. This is true also of many more complex reac­tions.