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Electrochemistry :an Introduction

Electrochemistry is the branch of chemistry deals with the chemical changes produced by and the production of electricity by chemical changes. Electricity is the movement of and is measured in Amps. The substances which allow an to flow through them are called electrical conductors; while those which do not allow any electric current to flow through them are called non-conductors(insulators).

Electrical conductors are of two types:

(A) Metallic conductors or electronic conductors: is an object or type of material that allow the flow of electrical conductors in one or more directions. A wire is a common electrical conductor. In general, belong to this category. The metals remain unchanged during the flow of current except warming. Here transfer of electric current is due to transfer of free electrons of outer shells without any transfer of matter. Example: Cu, Ag, Al,Au,Cr,Co etc. In metals, the mobile charged particles are electrons. Positive charges may also be mobile, such as the cationic of a battery, or the mobile protons of the proton conductors of a fuel cell. also conducts electricity due to presence of free e in its hexagonal sheet like structure.

(B) Electrolytic conductors: Also called electrolytic conductor. a conducting medium in which the flow of current is accompanied by the movement of matter in the form of . any substance that dissociates into ions when dissolved in a suitable medium or melted and thus forms a conductor of electricity The substances which in fused state or in aqueous solution allow the electric current to flow accompanied by chemical decomposition are called electrolytes. On the other hand substances which in fused state or in aqueous solution do not allow the electric current to flow are called non-electrolytes. Usually, electrovalent compounds are good electrolytes and covalent compounds are non-electrolytes (Glycerol, glucose etc.).The metal rod or foil dipped in , through which the electric current is conveyed, is called . The electrode on which negative ions (anions) arrive are called positive electrode or anode. Similarly the electrode on which positive ions (cations) arrive are called negative electrode or cathode.

Major differences between metallic and electrolytic conduction

Metallic conduction Electrolytic conduction

1. Conduction is due to movement of 1. Conduction is due to movement of electrons ions(Flow of electricity takes place by the decomposition of substance) 2. No chemical change takes place(flow of electricity takes place without the 2. Ions get oxidized or reduced at decomposition of substance

3. No transfer of matter Occurs 3. Transfer of Matter occurs in the form of ions 4. Resistance Temperature(conduction decreases with increase of temperature) 4. Resistance (conduction 5-Ohm,s law is followed increases with increase of temperature)

6- Faraday’s law is not followed 5-Ohm,s law is followed

6. Faraday’s law is followed

Classification of electrolytes Examples of strong and weak electrolytes are given below:

Strong Electrolytes strong acids HCl, HBr, HI, HNO3, HClO3, HClO4,

and H2SO4

strong bases NaOH, KOH, LiOH, Ba(OH)2, and

Ca(OH)2

salts NaCl, KBr, MgCl2, and many, many more

Weak Electrolytes

weak acids HF, HC2H3O2 (acetic acid), H2CO3

(carbonic acid), H3PO4 (phosphoric acid), and many more

weak bases NH3 (ammonia), C5H5N (pyridine), and several more, all containing "N

Semiconductor is a material that has a resistivity value between that of a conductor and an . The conductivity of a material can be varied under an external electrical field. Devices made from semiconductor materials are the foundation of modern electronics, including , computers, telephones, and many other devices. Semiconductor devices include the transistor, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier, and digital and analog integrated circuits. Solar photovoltaic panels are large semiconductor devices that directly convert light energy into electrical energy. In a metallic conductor, current is carried by the flow of electrons. In , current can be carried either by the flow of electrons or by the flow of positively-charged "holes" in the structure of the material. There are many examples of semiconductors such as Si,Ge,SnO2,TiO2,ZnO,Cds,CdSe, and many more

Electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it nearly impossible to conduct an electric current under the influence of an . This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors. The common examples of insulators are paper and mica glass.

Comparison between conductor, insulator and semiconductor by Energy

Difference between conductor, insulator and semiconductor

Conductor Insulator Semiconductor The conductivity of The conductivity of The conductivity of conductor is very high insulator is very low semiconductor is moderate It has very low resistivity It has very high resistivity It has moderate resistivity. It has no forbidden gap It has large forbidden It has small forbidden gap gap. Conductor has positive Insulator has negative Semiconductor has temperature coefficient of temperature coefficient of negative temperature resistance resistance coefficient of resistance In conductor, both the In insulator, effect of In semiconductor, effect effect of resistance and resistance is decreases of resistance is decreases temperature are and effect of temperature and effect of temperature increases is increases is increases. There is large number of There is small number of There is moderate electrons available for electrons available for number of electrons conduction conduction. available for conduction.

Some practical units used in electrochemistry:

The units obtained in electrochemistry are derived from System International(SI).The important units are listed as following:

Joule(J): It is the unit of energy and may defined as It is equal to the energy transferred (or work done) to an object when a force of one newton acts on that object in the direction of its motion through a distance of one meter (1 newton or N·m)

Coulomb(C): It is the unit of electrical charge(electricity )and may be defined as, t is the charge (symbol: Q or q) transported by a constant current of one ampere in one second:

it is also the amount of excess charge on a of one farad charged to a potential difference of one

1 Faraday (F) = 96500 Coulomb e-= electro charge=F

Faraday (F): is defined as the charge on one mole of electrons

Ampere(A or amp): It is the unit of electrical current ( measuring the rate of flow of electrons) and it defined as" The ampere is equivalent to one coulomb, i.e.,, ampere =(charge/time)

1A= 1 C /1

Ohm (Ω): It is the unit of electrical resistance and it defined as, an electrical resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere, the conductor not being the seat of any

Volt(V): It is the unit of , electric potential difference(), and electromotive force electrical(EMF) potential and may be defined as, One volt is defined as the difference in electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. It is also equal to the potential difference between two parallel, infinite planes spaced 1 meter apart that create an electric field of 1 newton per coulomb. Additionally, it is the potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it. It can be expressed in terms of SI base units (m,kg, s, and A) as .

It can also be expressed as amperes times ohms (current times resistance, Ohm