Electrochemical reactions are also called oxidation-reduction reactions or redox reactions for short.
The term oxidation itself now has a slightly different meaning than what it originally started out with. The term oxidation originally meant that something was combining with oxygen. If potassium combined with oxygen, the potassium was oxidized or went through the process of oxidation. So, oxidation meant the process of becoming combined with oxygen. When chemists started taking a look at what was going on, they looked at what oxygen did to these chemicals that were being oxidized. They found that the oxygen was pulling electrons away from the elements. Those elements were losing electrons to oxygen. In time the term oxidation became associated with loss of electrons instead of only combination with oxygen. So oxidation can occur with or without oxygen, but it must involve the loss of electrons.
The flip side of oxidation is reduction. If one chemical is losing electrons, another is gaining them. Gaining electrons is called reduction. That sounds contradictory, but it should make sense when we consider the oxidation states of the elements involved in the reaction, which we will do in a moment.
In order to recognize a redox reaction you have to look for evidence that electrons have moved from one chemical to another. You have to look for changes in the oxidation states of the elements involved. This requires that you be able to figure out the oxidation states of elements from formulas. The page on oxidation states gives you guidelines on how to do that if you are not already familiar with it. The page on terminology gives you some information on the meanings of various terms if you are not familiar with them.
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