ELECTROCHEMISTR Y What is electrochemistry? Electrochemistry is the
ELECTROCHEMISTR Y What is electrochemistry? Electrochemistry is the study of chemical reactions which take place at the interface of an electrode usually a solid, metal or semiconductor and an ionic conductor , the electrolyte. Electrochemistry deals with the interaction between electrical energy and chemical change.
History of electrochemistry English chemist john Daniel and physicist Michael faraday both credited as founders of electrochemistry today. The first germen physicist Otto von Guericke created the electric generater,which produced static electricity by applying friction in the machine. The English scientist William Gilbert spent 17 years experimenting with magnetism and to a lesser extent
electricity. Michael faraday john Danie l The french chemist charles francois de cisternry du fay had discovered two types of static electricity. William Nicholson and Johann Wilhelm Ritter
succeeded in decomposing water into hydrogen and oxygen by electrolysis. Ritter discovered the process of electroplating. William Hyde Wollaston made improvements to the galvanic cells. Orsteds discovery of the magnetic effect of electrical currents and further work on electromagnetism to others. Michael Faraday's experiments led him to state his two laws of electrochemistry and john Daniel invented primary cells.
Paul Heroult and Charles M.Hall developed an efficient method to obtain aluminum using electrolysis of molten alumina. Nernst developed the theory of the electromotive force and his equation known as Nernst equation, which related the voltages of a cell to its properties. Quantum electrochemistry was developed by Revaz dogonadeze and his pupils. Oxidation-Reduction The term redox stands for reduction- oxidation
It refers to electrochemical processes involving electron transfer to or from a molecule or iron changing its states. The atom or molecule which loses electrons is known as the reducing agent. The substance which accepts the electrons is called the oxidizing agent. Balancing redox reactions Acidic medium Example of manganese reacts with sodium bismuthate Unbalanced reaction: Mn2+(aq) + NaBiO3(s) Bi3+(aq) + MnO4(aq)
+ 2+ Basic medium Example of reaction between potassium permanganate and sodium sulfite. Unbalanced reaction: KMnO4 + Na2SO3 + H2O MnO2 + Na2SO4 + KOH Reduction:
3 e + 2 H2O + MnO4 MnO2 + 4 OH Oxidation: 2 OH + SO32 SO42 + H2O + 2 e 6 e + 4 H2O + 2 MnO4 2 MnO2 + 8 OH 6 OH + 3 SO32 3 SO42 + 3 H2O + 6e Equation balanced: 2 KMnO4 + 3 Na2SO3 + H2O 2 MnO2 + 3 Na2SO4 + 2 KOH Neutral medium Method to complete combustion of propane. Unbalanced reaction: C3H8 + O2 CO2 + H2O
Reduction: 4 H+ + O2 + 4 e 2 H2O Oxidation: 6 H2O + C3H8 3 CO2 + 20 e + 20 H+ 20 H+ + 5 O2 + 20 e 10 H2O 6 H2O + C3H8 3 CO2 + 20 e + 20 H+ Equation balanced: C3H8 + 5 O2 3 CO2 + 4 H2O Standard electrode potential To allow prediction of the cell potential, tabulations of standard electrode potential are available.
Tabulations are referenced to the standard hydrogen electrode. The standard hydrogen electrode undergoes the + reaction (aq) 2 2H +2e H
Standard electrode potentials are usually tabulated as reduction potentials. The reactions are reversible and the role of particular electrode in a cell depends on the relative oxi./red. Potential of both electrodes. The cell potential is then calculated as the sum of reduction potential for cathode and the oxidation potential for anode. For example, the standard electrode Cell diagram potential
for a copper electrode is: + 2+ Pt(s) | H2 (1 atm) | H (1 M) || Cu (1 M) | Cu(s) Ecell = Ered (cathode) Ered (anode) Gibbs free energy and cell potential
Though cell potential Cell and get electricity n faraday in the-nFE cell: = cell For standard cell, this equation can we written G 0
= 0 -RTlnK=-nFE cell Though produce of electric energy converted into electric work, Wmax= Welectrical= -nFEcell Nernst equation E(Mn+|M)=E0(Mn+|M)-
ln But solid M concentrate constant E(Mn+|M)=E0(Mn+|M)- ln Example of Daniel cell For cathode : E(Cu2+|Cu)=E0(Cu2+|Cu)- ln : E(Zn2+|Zn)=E0(Zn2+|Zn)-
ln Electrical resistivity It is an intrinsic property that quantities how strongly a given material opposes the flow of electrical current. Many resistors and conductors have a uniform cross section with a uniform flow of electric current and made of one material The electrical resistivity defined Electrical conductivity
The reciprocal of electrical resistivity, and measures a materials ability to conduct an electric current. It is commonly represented by Conductivity is defined as Conductivity SI units of Siemens per meter. Molar conductivity Molar conductivity is defined as the conductivity of an electrolyte solution divided by the molar concentration of the electrolyte,
and so measures the efficiency with which a given electrolyte conducts electricity in solution. From definition, the molar conductivity Two cases should be distinguished: Strong eletrolyte and weak electrolyte For strong electrolyte Salts, strong acids and strong bases, the molar conductivity depends only weakly on concentration. For weak electrolyte
The molar conductivity strongly depends on concentration. The more dilute a solution, the greater its molar conductivity, due to increased ionic dissociation. For weak electrolyte obeys Oswald's dilulation law. Kohlrauschs law of independent migration of ions High accuracy in dilute solutions, molar conductivity is composed of individual
contributions of ions. Limiting conductivity of anions and cations are additive, the conductivity of a solution of a salt is equal to the sum of conductivity contributions from the cation and anion 0 0 0 m=v+ + + v- -
Battery Many types of battery have been commercialized and represent an important practical application of electrochemistry. Early wet cells powered the first telegraph and telephone systems, and were the source of current for electroplating. The zinc-manganese dioxide dry cell was the first portable, non-spill able battery type that made flashlights and other portable devices practical. The mercury battery using zinc and mercuric
oxude provided higher levels of power and capacity than the original dry cell for early electronic devices. Lead-acid battery was secondary battery. The electrochemical reaction that produced current was reversible, allowing electrical energy and chemical energy to be interchanged as needed. Lead-acid cells continue to be widely used in automobiles. The lithium battery, which does not use water
in the electrolyte, provides improved performance over other types. Rechargeable lithium ion battery is an essential part of many mobile devices. Corrosion Corrosion is the term applied to steel rust caused by an electrochemical process. Corrosion of iron in the form of reddish rust, black tarnish on silver, red or green may be appear on copper and its alloys, such as brass.
Prevention of corrosion Coating Metals can be coated with paint or other less conductive metals. This prevents the metal surface from being exposed to electrolytes. Scratches exposing the metal substrate will result in corrosion. Sacrificial anodes The method commonly used to protect a structural metal is to attach a metal which is
more anodic than the metal to be protected. This forces the structural metal to be catholic thus spared corrosion. it is called sacrificial. Zinc bars are attached to various locations on steel ship hulls to render the ship hull catholic. Other metal used magnesium. Electrolysis The spontaneous redox reactions of a conventional battery produce electricity through the different
chemical potentials of the cathode and anode in the electrolyte. Electrolysis requires an external source of electrical energy to include a chemical reaction , and this process takes place in a compartment called an electrolytic cell. Electrolysis of molten sodium chlorine When molten, the salt sodium chloride can be electrolyzed to yield metallic sodium
and gaseous chlorine. This process takes place in a special cell named Downs cell. Reactions that take place at Down's cell are the following Anode (oxidation): 2 Cl Cl2(g) + 2 e Cathode (reduction): 2 Na+(l) + 2 e 2 Na(l) Overall reaction: 2 Na+ + 2 Cl(l) 2 Na(l) + Cl2(g) This process can yield large amounts of metallic sodium and gaseous chlorine, and widely used on mineral dressing and metallurgy industries.
Quantitative electrolysis and Faradays law Quantitative aspects of electrolysis were originally developed by Michel faraday . Faraday is also credited to have coined the terms electrolyte. Electrolysis among many others while studying analysis of electrochemical reactions. Faraday advocate of the law of conservation of energy.
First law The mass of products yielded on the electrodes was proportional to the the value of current supplied to the cell, the length of time the current existed, and the molar mass of the substance analyzed. The amount of substance deposited on each electrode of an electrolytic cell is directly proportional to the quantity of electricity passed m= through the cell. Second law
The amounts of bodies which are equivalent to each other in the ordinary chemical action have equal quantities of of electricity naturally associated with them. The quantities of different elements deposited by a given amount of electricity are in the ratio of the chemical equivalent weights Applied aspects of electrochemistry Industrial electrolytic processes Electrochemical Reactors Batteries Fuel cells
Some Electrochemical Devices Electrochemical Methods of Analysis Branch of electrochemistry Photo electrochemistry It is subfield of study within physical chemistry. The interest in this domain is high in the context of development of renewable energy conversion and storage technology. The effects of luminous radiation on the properties of electrodes and on electrochemical reactions are the subject of
photo electrochemistry Semiconductors electrochemistry Semiconductor material has a band gap and generates a pair of electron and hole per absorbed photon if the energy of the photon is higher than the band gap of the semiconductor. This property of semiconductor materials has been successfully used to converted solar energy into electrical energy by photovoltaic devices. Semiconductor-electrolyte interface When a semiconductor comes into contact with a liquid, to maintain electrostatic equillibrium
There will be a charge transfer between the semiconductor and liquid phase,if formal redox potential of redox species lies inside semiconductor band gap. At thermodynamic eqilibrium, the fermi level of semiconductor and the formal redox potential of redox species and between interface semiconductor. This introduce n-type semiconductor and p-type semiconductor. This semiconductor used as photovoltaic device similar to solid state p-n junction devices.
Both n and p type semiconductor can used as photovoltaic devices to convert solar energy into electrical energy and are called photoelectrical cells Boielectrochemistry It is branch of electrochemistry and biophysical chemistry concerned with topics like cell electron-proton transport, cell membrane potentials and electrode reactions of redo enzymes. Bioelectrochemistry is a science at the many junctions of sciences.
Nanoelectrochemistry Nanoelectrochemistry is a branch of electrochemistry that investigates the electrical and electrochemical properties of materials at the nanometer size regime. Nanoelectrochemistry plays significant role in the fabrication of various sensors, and devices for detecting molecules at very law concentrations. The term electrochemical nanostructuring can
be used to mean different things. This term is employed to refer to generation at will of nanostructure on electrode surface, involving a given positioning with a certain precision The term nanostructure is used to describe the generation of nanometric patterns with move or less narrow size distribution and a periodic or random ordering on the surface. But without control on the spatial location of the nanostructure. Application of electrochemistry There are various extremely important
electrochemical processes in both nature and industry. The coating of objects with metals or metal oxides through electro deposition and the detection of alcohol in drunken drivers through the redox reaction of ethanol. Diabetes blood sugar meters measure the amount of glucose in the blood through its redox potential. The generation of chemical energy through photosynthesis in inherently an electrochemical
process. Production of metals like aluminium and titanium from their ores. For Photo electrochemistry Artificial photosynthesis Regenerative cell or Dye-sensitized cell Photo electrochemical splitting of water For Boielectrochemistry Some of different experimental techniques that can be used to study bioelectrochemical problems. Ampermetic of biosensors
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