The electrochemistry is based on the redox reactions. Now we will see how we can use different substances electrochemical. We know that there are substances which deliver electrons very easy (reducing agent) and they are not noble. There are also substances which take electrons (oxidizing agent) and they are noble. Lithium for example delivers an electron* because then it reachs noble gas configuration. Oxygen reachs the noble gas configuration by taking two electrons and so it is much more noble than lithium. Because of this facts there is the electromotive series. In this electromotive series every substance has got a certain place. On the one side there are the strong reducing agents and on the other side there are the strong oxidizing agents. Noble gases are not in this electromotive series* because they have already reached the noble gas configuration. The least noble substance in this electromotive series is lithium. The strongest oxidizing agent in the electromotive series is fluorine and so it is the nobliest substance in the electromotive series. This electromotive series says that there is a voltage gradient or a difference of potential between two different substances. This electromotive series bases on hydrogen. The definition says that hydrogen has got a voltage of 0 Volt.