Redox Reactions

Law of Conservation of Energy:

No energy is created, nor destroyed, it is transformed or transferred.

Yes, and in a chemical reaction? aren't there like several exchange of electrons?

If each atom or ion of a chemical reaction is oxidized, that another must be reduced. When this happens we have a redox reaction.

Redox reactions are not a type of reaction, like formation, or decomposition. 

Actually, all the types of reactions may be redox reactions.

To understand this concept better let's use this simple single-replacement reaction:

Zn(s)+CuSO4(aq)=Cu(s)+ZnSO4(aq)

Lets take away the spectators, which, in this case are the SO4 ions.

You obtain 

Zn(s) + Cu+2(aq) = Cu(s)+Zn+2 

As you see, Zinc lost electrons, it became positive, thus got oxidized. Copper, gained two electrons, since it was a cation and became a single atom. Therefore it was reduced. 

Well, we know that the electrons ran away from Zn to Cu, so what do we do about it?

Zinc is called the reducing agent, the one that donated electron, and the one the underwent oxidation, while copper is the oxidizing agent, the one that accepeted electrons, undergoes reduction.