Electrochemistry is the study of production of electricity from energy released during spontaneous chemical reactions and the use of electrical energy to bring about non-spontaneous chemical transformations.
An electrochemical cell is a device that can generate electrical energy from the chemical reactions occurring in it, or use the electrical energy supplied to it to facilitate chemical reactions in it.
These devices are capable of converting chemical energy into electrical energy, or vice versa.
A galvanic cell is a type of electrochemical cell. It is used to supply electric current by making the transfer of electrons through a redox reaction. A galvanic cell is an exemplary idea of how energy can be harnessed using simple reactions between a few given elements.
It is measured with the help of a reference electrode known as the standard hydrogen electrode (abbreviated to SHE). The electrode potential of SHE is 0 Volts.
The standard electrode potential of an electrode can be measured by pairing it with the SHE and measuring the cell potential of the resulting galvanic cell.
The Nernst Equation enables the determination of cell potential under non-standard conditions. It relates the measured cell potential to the reaction quotient and allows the accurate determination of equilibrium constants (including solubility constants).
In a galvanic cell, the Gibbs free energy is related to the potential by: ΔG°cell = −nFE°cell. If E°cell > 0, then the process is spontaneous (galvanic cell). If E°cell < 0, then the process is nonspontaneous (electrolytic cell).
Conductance) of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is siemens per meter (S/m). The SI unit of conductivity is S/m and, unless otherwise qualified, it refers to 25 °C.
Conductance is a property of electrolytic solutions which indicates how well an electrolyte can conduct electricity. Its value is numerically equal to the reciprocal of the resistance to the flow of electricity through the solution. I.e. C = 1/R.
The conductivity of electrolytic (ionic) solutions depends on:
(i) the nature of the electrolyte added
(ii) size of the ions produced and their solvation
(iii) the nature of the solvent and its viscosity
(iv) concentration of the electrolyte
(v) temperature (it increases with the increase of temperature).
Conductivity (or specific conductance) of an electrolyte solution is a measure of its ability to conduct electricity.
The SI unit of conductivity is S/m and, unless otherwise qualified, it refers to 25 °C. More generally encountered is the traditional unit of μS/cm.
The commonly used standard cell has a width of 1 cm, and thus for very pure water in equilibrium with air would have a resistance of about 106 ohms, known as a megohm. Ultra-pure water could achieve 18 megohms or more
Molar conductivity has the SI unit S m2 mol−1. Older publications use the unit Ω−1 cm2 mol−1.
Molar conductivity increases with decrease in concentration as the total volume, V, of a solution containing one mole of electrolyte also increases.
Upon dilution, the concentration decreases. When the concentration approaches zero, the molar conductivity of the solution is known as limiting molar conductivity, Ë°m.
An electrolytic cell is a kind of electrochemical cell. It is often used to decompose chemical compounds, in a process called electrolysis—the Greek word lysis means to break up.
Important examples of electrolysis are the decomposition of water into hydrogen and oxygen, and bauxite into aluminium and other chemicals.
Electrolytic cells are used for all kinds of things: electroplating metals, recharging a battery, and separating pure metals from metallic compounds.
When electrolytic cells are used to separate chemical compounds, the process is known as electrolysis.
Electrolysis is the passing of a direct electric current through an electrolyte producing chemical reactions at the electrodes and decomposition of the materials. The main components required to achieve electrolysis are an electrolyte, electrodes, and an external power source.
When ions reach an electrode, they gain or lose electrons. As a result, they form atoms or molecules of elements:
Molten lead bromide, PbBr2(l), is an electrolyte. During electrolysis:
Batteries are the most common power source for basic handheld devices to large scale industrial applications. There are mainly two types of batteries.
A primary cell is a battery that is designed to be used once and discarded, and not recharged with electricity and reused like a secondary cell. In general, the electrochemical reaction occurring in the cell is not reversible, rendering the cell unrechargeable. Primary batteries are single-use galvanic cells that store electricity for convenient usage, usually showing a good shelf life. Examples are zinc–carbon (Leclanché) cells, alkaline zinc–manganese dioxide cells, and metal–air-depolarized batteries. Primary lithium cells are now available.
A secondary cell after use can be recharged by passing current through it in the opposite direction so that it can be used again. A good secondary cell can undergo a large number of discharging and charging cycles. The most important secondary cell is the lead storage battery commonly used in automobiles and invertors. It consists of a lead anode and a grid of lead packed with lead dioxide (PbO2) as cathode. A 38% solution of sulphuric acid is used as an electrolyte.
Galvanic cells that are designed to convert the energy of combustion of fuels like hydrogen, methane, methanol, etc. directly into electrical energy are called fuel cells. A fuel cell consists of two electrodes—a negative electrode (or anode) and a positive electrode (or cathode)—sandwiched around an electrolyte.
A typical fuel cell works by passing hydrogen through the anode of a fuel cell and oxygen through the cathode. At the anode site, a catalyst splits the hydrogen molecules into electrons and protons.
Fuel cells are used for primary and backup power for commercial, industrial and residential buildings and in remote or inaccessible areas. They are also used to power fuel cell vehicles, including forklifts, automobiles, buses, boats, motorcycles and submarines.
Corrosion is when a refined metal is naturally converted to a more stable form such as its oxide, hydroxide or sulphide state this leads to deterioration of the material. Corrosion slowly coats the surfaces of metallic objects with oxides or other salts of the metal.
The rusting of iron, tarnishing of silver, development of green coating on copper and bronze are some of the examples of corrosion. It causes enormous damage to buildings, bridges, ships and to all objects made of metals especially that of iron. We lose crores of rupees every year on account of corrosion.
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