 | Electrochemistry: Encyclopedia - Electrochemistry
Electrochemistry
Electrochemistry is a branch of chemistry and studies the reactions that can take place at the interface of an electronic conductor (the electrode, which can be a metal or a semiconductor including graphite) and an ionic conductor (the electrolyte).
If a chemical reaction is caused by an external voltage, or if a voltage is caused by a chemical reaction, as in a Battery (electricity), it is an electrochemical reaction. In general, electrochemistry deals with situations where an oxidation and a reduction reaction is separated in space. The direct charge transfer from one molecule to another is not the topic of electrochemistry.
Electrochemistry - History
The study of chemical reactions and electricity dates back since 1600s when english physician William Gilbert conducted experiments on magnetism, by early 1700s many european scientists were researching if electric current could be produced from chemical reactions; but it wasn't until mid-1780s when italian anatomist Luigi Galvani got the answer after studying frog legs. In his experiment Galvani fastened brass hooks between the spinal cord of a dissected frog and an iron railing. Later Galvani interpreted his results in terms of "animal electricity" and proclaimed that the muscle retained a nerveo-electrical fluid similar to that of an electric eel.
Activity series of metals, Bioelectricity, Electrochemical potential, Important publications in Electrochemistry, Redox titration
Electrochemistry - Principles
Electrochemistry - Oxidation and Reduction
The elements involved in an electrochemical reaction are characterized by the number of electrons each has. The oxidation state of an ion is the number of electrons it has accepted or donated compared to its neutral state (which is defined as having an oxidation state of 0). If an atom or ion donates an electron in a reaction its oxidation state is increased, if an element accepts an electron its oxidation state is decreased.
For example when sodium reacts with chlorine, sodium donates one electron and gains an oxidation state of +1. Chlorine accepts the electron and gains an oxidation state of ā1. The sign of the oxidation state (positive/negative) actually corresponds to the value of each ion's electronic charge. The attraction of the differently charged sodium and chlorine ions is the reason they then form an ionic bond.
The loss of electrons of a substance is called oxidation, and the gain of electrons is reduction. This can be easily remembered through the use of mnemonic devices. Two of the most popular are "OIL RIG" (Oxidation Is Loss, Reduction Is Gain) and "LEO" says "GER" (Lose Electrons: Oxidization, Gain Electrons: Reduction).
The substance which loses electrons is also known as the reducing agent, or reductant, and the substance which accepts the electrons is called the oxidizing agent, or oxidant. The oxidizing agent is always being reduced in a reaction; the reducing agent is always being oxidized.
The gain of oxygen, loss of hydrogen and increase in oxidation number is also considered to be oxidation, while the inverse is true for reduction.
A reaction in which both oxidation and reduction is occurring is called a redox reaction. These are very common; as one substance loses electrons the other substance accepts them.
Oxidation requires an oxidant. Oxygen is an oxidant, but not the only one. Despite the name, an oxidation reaction does not necessarily need to involve oxygen. In fact, even fire can be fed by an oxidant other than oxygen: fluorine fires are often unquenchable, as fluorine is an even stronger oxidant (it has a higher electronegativity than oxygen).
In the 1960sā1970s quantum electrochemistry was developed by Revaz Dogonadze and his pupils.
The International Society of Electrochemistry (ISE) was founded in 1949.
Electrochemistry - Spontaneity
A spontaneous electrochemical reaction can be used to generate an electrical current, in electrochemical cells. This is the basis of all batteries and fuel cells. For example, gaseous oxygen (O2) and hydrogen (H2) can be combined in a fuel cell to form water and energy (a combination of heat and electrical energy, typically).
Conversely, non-spontaneous electrochemical reactions can be driven forward by the application of a current at sufficient voltage. The electrolysis of water into gaseous oxygen and hydrogen is a typical example.
See also
- Activity series of metals
- Bioelectricity
- Electrochemical potential
- Important publications in Electrochemistry
- Redox titration
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