Electrochemistry is the area of Chemistry that studies the reactions that involve the transfer of electrons and the interconversion of chemical energy into electrical energy.
Electrochemistry is applied to the manufacture of many devices used in our daily lives, such as batteries, cell phones, flashlights, computers and calculators.
Oxidation Reactions
In electrochemistry, the reactions studied are those of redox. They are characterized by the loss and gain of electrons. This means that electron transfer from one species to another.
As its name implies, redox reactions occur in two steps:
- Oxidation: Loss of electrons. The element that causes oxidation is called an oxidizing agent.
- Reduction: Electron gain. The element that causes the reduction is called the reducing agent.
However, to know who gains and who loses electrons, you must know the oxidation numbers of the elements. See this redox example:
Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g)
The Zinc Element (Zn2+) is oxidized by losing two electrons. At the same time, it caused the reduction of the hydrogen ion. Hence, it is the reducing agent.
The (H) ion+) gains an electron, undergoing reduction. As a result, it caused the oxidation of zinc. It is the oxidizing agent.
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Batteries and Electrolysis
The study of electrochemistry comprises batteries and electrolysis. The difference between the two processes is energy transformation.
- THE cell converts chemical energy into electrical energy, spontaneously.
- THE electrolysis converts electrical energy into chemical energy, so not spontaneously.
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Stacks
The cell, also called an electrochemical cell, is a system where the redox reaction takes place. It is composed of two electrodes and an electrolyte, which together produce electricity. If we connect two or more batteries together, a battery is formed.
The electrode is the solid conductive surface that enables the exchange of electrons.
- The electrode in which oxidation occurs is called the anode, representing the negative pole of the battery.
- The electrode on which the reduction takes place is the cathode, the positive pole of the battery.
The electrons are released at the anode and follow a conducting wire to the cathode, where reduction occurs. Thus, the flow of electrons goes from anode to cathode.
The electrolyte or salt bridge is the electrolyte solution that conducts electrons, allowing their circulation in the system.
In 1836, John Fredric Daniell built a system that became known as Daniell Pile. He interconnected, with a metallic wire, two electrodes.
One electrode consisted of a metallic zinc plate, immersed in an aqueous solution of zinc sulfate (ZnSO4), representing the anode.
The other electrode consisted of a metallic copper plate (Cu), immersed in a solution of copper sulfate (CuSO4), represented the cathode.
At the cathode copper reduction occurs. Meanwhile, in the anode the oxidation of zinc takes place. According to the following chemical reaction:
Cathode: ass2+(aq) + 2e- | → Cu0(s)|
anode: Zn0(s) | → Zn2(aq) + 2e-|
General Equation: Zn0(s) + Cu2+(aq) | → Cu0(s) + Zn2+(aq)|
The "|" represents the phase differences between reactants and products.
Electrolysis
THE electrolysis it is the oxidation-reduction reaction that occurs in a non-spontaneous way, caused by the passage of electric current coming from an external source.
Electrolysis can be igneous or aqueous.
Igneous electrolysis is one that is processed from a molten electrolyte, that is, by the fusion process.
In aqueous electrolysis, the ionizing solvent used is water. In aqueous solution, electrolysis can be performed with inert electrodes or active (or reactive) electrodes.
applications
Electrochemistry is very present in our daily lives. Some examples are:
- Reactions in the human body;
- Manufacture of various electronic devices;
- Charging of batteries;
- Electroplating: coating of iron and steel parts with metallic zinc;
- Various types of application in the chemical industry.
Rust in metals is formed by the oxidation of metallic iron (Fe) to iron cation (Fe2+) when in the presence of air and water. We can consider rust as a type of electrochemical corrosion. The coating with metallic zinc, through the electroplating process, prevents the iron from coming into contact with the air.
Exercises
1. (FUVEST) - I and II are equations of reactions that occur spontaneously in water, in the sense indicated, under standard conditions.
I. Fe + Pb2+ → Fe+2 + Pb
II. Zn + Fe2+ → Zn2+ + Fe
Analyzing such reactions, alone or together, it can be said that, under standard conditions,
a) electrons are transferred from Pb2+ for Fe.
b) spontaneous reaction must occur between Pb and Zn2+.
c) Zn2+ must be better oxidizer than Fe2+ .
d) Zn must spontaneously reduce Pb2+ to Pb.
e) Zn2+ must be better oxidizer than Pb2+.
d) Zn must spontaneously reduce Pb2+ to Pb.
2. (Unip) Iron or steel objects can be protected from corrosion in several ways:
I) Covering the surface with a protective layer.
II) Putting the object in contact with a more active metal such as zinc.
III) Putting the object in contact with a less active metal such as copper.
Are correct:
a) only I.
b) only II.
c) only III.
d) only I and II.
e) only I and III
d) only I and II.
3. (Fuvest) In a pile of the type commonly found in supermarkets, the negative pole is constituted by the outer coating of zinc. The semi-reaction that allows zinc to function as a negative pole is:
a) Zn+ + and- → Zn
b) Zn2+ + 2e- → Zn
c) Zn → Zn+ + and-
d) Zn → Zn2+ + 2e
e) Zn2+ + Zn → 2Zn+
d) Zn → Zn2+ + 2e
