Electrochemistry
From MyMCAT
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the electrolyte), and which involve electron transfer between the electrode and the electrolyte or species in solution.
If a chemical reaction is driven by an external applied voltage, as in electrolysis, or if a voltage is created by a chemical reaction as in a battery, it is an electrochemical reaction. Chemical reactions where electrons are transferred between molecules are called oxidation/reduction (redox) reactions. In general, electrochemistry deals with situations where oxidation and reduction reactions are separated in space or time, connected by an external electric circuit to understand each process.
Contents |
Oxidation State
The atoms, ions, or molecules involved in an electrochemical chemical reactions are characterized by the number of electrons each has relative to its number of protons -- this is the molecules oxidation state and is denoted by a + or a -. Thus the superoxide ion, O2-, has an oxidation state of -1.
Oxidation and Reduction
The loss of electrons from an atom or molecule is called oxidation, and the gain of electrons is reduction. This can be easily remembered through the use of mnemonic devices. The most popular is "LEO" the lion says "GER" (Lose Electrons: Oxidization, Gain Electrons: Reduction).
Oxidation and reduction always occur in a paired fashion such that one species is oxidized when another is reduced. This paired electron transfer is called a redox reaction.
Oxidizing Agent and Reducing Agent
The atom or molecule which loses electrons is known as the reducing agent, and the substance which accepts the electrons is called the oxidizing agent. The oxidizing agent is always being reduced in a reaction; the reducing agent is always being oxidized. Oxygen is a common oxidizing agent, but not the only one. Despite the name, an oxidation reaction does not necessarily need to involve oxygen.
For reactions involving oxygen, the gain of oxygen implies the oxidation of the atom or molecule to which the oxygen is added. Conversely, loss of oxygen or gain of hydrogen implies reduction.
See Also
- Electrochemical Cells Introduction - An introduction (with sample questions) to electrochemistry in galvanic and electrolytic cells.
- Oxidation Numbers - An introduction to oxidation states, including the general concepts and rules for how to identify and assign oxidation numbers.
