Electrocheistry research recovered

1. Electrochemistry

2. Electricity
• Electric Charge: the basis of electricity
• Charge is a property possessed by matter . It consist of positive
charge and negative charge.
• Charge is measured in coulombs,represented by C
• Qo
= 1.6022 x10-19 C
• Charge is not found in isolation, it always accompanies matter.

3. • fundamental particles as the proton H+ and the electron e- possess
single charges.eg sodium Na+ , chloride Cl- , and hydronium H3O+ ions
• Even neutral molecules, which have no net charge, are held together
electrically and have charges on their surfaces.
• Eg one side of the water molecule pictured has a negative region, the
other side being positively charged. Such structures are called dipoles
• The red surface is positively charged whereas blue surface are
negatively charged

4. • The electrical force, f, between two charges Q1 and Q2 and r12 as the
distance between the two charges.
• force f obeys Coulomb’s law
• The SI unit of force is the newton N.
ε is the permittivity of the medium,
• What Is Coulomb’s Law?
• According to Coulomb’s law, the force of attraction or repulsion between
two charged bodies is directly proportional to the product of their
charges and inversely proportional to the square of the distance between
them.

5. principle of electroneutrality
• The law of electroneutrality states that in any single ionic solution a
sum of negative electrical charges attracts an equal sum of positive
electrical charges.
• Eg an ionic solution of nacl where Na+ ions are attracted towards cl-
ions

6. Charges at Rest: electric field and electrical
potential
• An electric field is said to exist around each charge. The electric field
is a vector; that is, it has both direction and strength.
• Field created by positive charge is away from charge whereas field
created by negative charge is towards the charge.

7. • The strength of an electric field at a point can be assessed by placing a
very small positive “test charge” Q test at the point.
• The test charge will experience a small coulombic force
• The electric field strength X, is then defined
•
• unit of field will be newtons per coulomb, NC-1
• for any static charge distribution, it is possible to calculate field
strengths using Coulomb’s law.

8. Force and electric field both are a vector quantity
Two geometries are considered
• The first has spherical symmetry and second is planar symmetry
• The first has spherical symmetry, which means that all properties are
uniform on any sphere centered at the point r=0

9. According to the inverse-square law: at double the distance from a point
source the field is one-fourth. The distance R is given by
•
The inverse-square law does not apply to the field in planar symmetry
In panar the field between two charged planes, such as electrodes.The field
strength caused by that plane, at a distance can be shown
•
• note : inverse-square law is any scientific law stating that a specified
physical quantity is inversely proportional to the square of the distance

10. • The concept of a small “test charge” is a valuable fiction; it is also used to
define electrical potential
• Imagine that we place a test charge at point A, and move it a small
distance r towards a much larger fixed charge
Work is done which is given by
Negative sign indicates it is in opposite direction

11. • Electric potential (V) exist between two both point A and B
• Difference between the potential is given
Where X = electric potential
In differential notation, the equation becomes
The unit of electrical potential is the volt
In electrochemistry, electrical potential is a more convenient quantity than
electric field, in part because it is not a vector.

12. • The force on the moving test charge now varies along the journey, not
only because the field strength changes, but also because the angle
constantly alters as the charge moves
• We can define only differences in electrical potential. Worse, we can
define differences in the electrical potential only between points that
lie within phases of the same (or very similar) compositions
• The symbol ρ is generally used to represent volumetric charge density

13. • The local field gradient is simply the volumetric charge density there
divided by the permittivity
•
• for a spherically symmetric geometry

14. Capacitance and Conductance
• Materials may be divided loosely into two classes:
• electrical conductors and insulators
• Conductors allows the passage of electricity, and insulators do not.
• Conductors are further classified in to
• In electronic conductors conductivity is due to the presence of
mobile electrons.
• whereas the in ionic conductors the conductuctance is due to ions.

15. • All metals are electronic conductors, but some solid inorganic oxides
and sulfides also conduct electricity by electron flow.
• In Semiconductors the conductivity is due to p type n type conductors
• In p type the conductance is due to holes whereas in n type
conductance is due to extra electron
• In p type semiconductor , it is actually an electron that moves into an
existing hole and thereby creates a new hole at its former site
• Pi-electrons are the charge carriers in some other materials,
• Eg graphite and newer synthetic conductive polymers.
• Certain crystalline organic salts known as organic metals, also conduct
by virtue of electron motion.

16. ionic conductors, which possess conductivity by virtue of the motion of
anions and/or cations eg solutions of electrolytes
Eg Na+ and Cl-
1-butyl-3-methylimidazoliumhexafluorophosphate
Stoichiometric compounds contain two or more elements in atom
ratios that are stricly whole numbers.
eg Water contains exactly twice as many H atoms as O atoms

17. • Nonstoichiometric solids associated with defects in the crystal lattice,
or be introduced artificially with a small quantity of a dopant
• In organic compounds having alternating single and double bonds in
chains or rings, including abnormal electrical conductivity.
• Such electrons are described as “pi-electrons”
• Thus some inorganic compound has electrical conductivity due to
presence of pi electron

18. • inorganic salts generally have much high melting points and conduct
only at elevated temperatures
• Eg ZrO2 , which at high temperatures, allows oxide ions, O2-, to migrate
through its lattice a an anion
• Eg LaF3 , crystals that have been “doped” by a very small addition of
europium fluoride, EuF2
• dopant contributes fewer F2-ions to the lattice than its host
• “fluoride ion holes” which can move exactly as holes in p-type
semiconductors.
• Such crystals find applications in the fluoride ion sensor

19. • A few materials permit the flow of electricity by both electronic and
ionic conduction
Eg 1)hot gases known as plasmas
2)sodium metal dissolves in liquid ammonia
It contains sodium Na+ cations and solvated electrons both of which
are mobile and share duties as charge carriers.
3)Hydrogen dissolved in palladium metal; there is conduction by the
migration of protons (hydrogen ions) as well as by electrons

21. • voltage source use to measure electric potential and it has two
terminals, one of which (often colored red) is at a more positive
electrical potential than the other
• voltmeters, also a device that can measure electrical potential
differences. Both of them are electronic device

22. • Parallel plates are plates which store charge when the switch is open
• Because of the electroneutrality principle electrons arrive on the inward-
facing surface on the R.H.S bcoz the electron are withdrawn .
• From the L.H.S plates such a parallel distribution of charges produces a
uniform electric field of strength X in the space between the plates which is
given by
• Where ε is the permittivity of the medium
• between the plates

23. To carry a test charge a distance L, from a point adjacent to the negatively
charged plate to a second point adjacent to the positive plate, will require work
w
The potential difference
is the potential difference between two points in the medium
The voltmeter shown measures the difference ∆E in potential between the two
metal plates.

24. The parallel plates that is able to store electric charge is called a capacitor.
The stored charge is
The ratio of the potential difference to the charge it stores is called the
capacitance of the capacitor and is given the symbol C
The unit of capacitance is the farad, F
One farad equals one coulomb per volt

25. • what happens when an insulator is placed between the parallel plates
of a capacitor
• Permittivities vary greatly, so that the capacitor now has a larger
capacitance and stores more charge for a given voltage.
• when the insulator has a dipolar molecule, such as the organic liquid,
acetonitrile, CH3CN or the water molecule This molecule has a
positive end and a negative end and, in an electric field, such
molecules tend to align themselves
• The effect is to create localized fields within the insulator that oppose,
and partially neutralize, the imposed field, so that more external
charge is required to reach the applied voltage ∆E.
• Insulators that behave in this ways are often called dielectrics.

26. • Now if we place an electronic conductor between the plates. The electrons
are now able to pass freely from the negative plate into the conductor, and
from the conductor into the positive plate.
• Electrons being negative, their passage from right to left through the
conductor corresponds to electric charge flowing from left to right.
• We say an electric current, I, flows through the conductor:
• It expresses the rate at which charge passes through the conductor
• Electric current is measured in the ampere,
• one ampere corresponding to the passage of one coulomb in a time t of
one second

27. • The same flow of electricity that occurs in
the conductor is also experienced in the
wires and plates that constitute what is
known as the circuit
• ammeter, an electronic device that
measures electric current,
• A quantity equal to the current divided by
the cross-sectional area through which it
flows, is the current density,
•
• It is measured in amperes per square meter,
A m-2

28. • The ratio of the current density flowing in a conductor to the field that creates
it is called the conductivity k of the material
• Resistance can be measured
• Conductivity (or specific conductance) of an electrolyte solution is a measure
of its ability to conduct electricity
• Resistivity refers to the electrical resistance of a conductor of a particular unit
cross-sectional area and unit length

29. • when an electric field is applied to an ionic conductor, for example by
applying a voltage between two plates that sandwich the conductor
• If the ionic conductor contains mobile ions of two types, cations and
anions, then the ions will move towards left and right
• As the moving ions approach the impenetrable plates, they are halted
and accumulate there.
• The two sheets of accumulating ions themselves create a field that
opposes that caused by the plates
• Eventually the motion ceases because the two fields entirely cancel
and leave the interior of the conductor field-free.

30. • We now have four sheets of charge: two electronic and two ionic. At
the surface of each plate a layer of ions confronts a layer of electronic
charge of equal magnitude but opposite sign. This is called a double
layer

31. • Mobilities: the movement of charged particles in an electric field
• consider the case of a material with a sole charge carrier, its charge being a
single positive charge Q0 , such as a hole in a p-type semiconductor
• Some thought shows that this current can be equated to the product of
four terms
• The first of these is the number density of charge carriers concentration c
of the carrier multiplied by Avogadro’s constant ,
• NA, equal to 6.0221 × 1023 mol-1
• The second and third right-hand terms are simply A and Q0 respectively
• The fourth is the average velocity with which the carrier moves in the x
direction

32. • The product of Avogadro’s number and the elementary charge and
this product is given the symbol F and the name Faraday’s constant
Faraday’s constant provides the quantitative connection between
chemistry and electricity.
Eg In one mole of sodium chloride, the total charge on the sodium
ions, Na+ , is 96485 coulombs and, of course, there are -96485 C on the
chloride ions, Cl-

33. • The velocity of the charge carrier is proportional to the current, and
therefore to both the electric field and the conductivity
• The ratio of the average velocity of the moving charge carriers to the
field that causes that motion is known as the mobility u of the carrier
• A carrier i that has a charge of Qi is said to have a charge number
• For example, electrons e- and calcium ions Ca2+ have charge numbers of
• -1 and +2 respectively
• mobilities are affected by such factors as temperature and the medium
in which the charge carriers

34. • Electrical Circuits: models of electrochemical behavior
• A device that is fabricated to have a stable resistance is known as a
resistor it is represented in circuit diagrams by
• Capacitor is repreented by
• Resistors and capacitors are examples of circuit elements.
• When two or more circuit elements are connected in parallel they
experience the same voltage, conversely they are in series if they
experience the same current.

35. • Resistor and a capacitor Connected in parallel
• it provides a model of materials that
• have both dielectric and conductive properties.
• when load is connected the switch is closed?
• Energy, provided by the voltage source,has been
• stored in the capacitor.
• The resistor, converts electrical energy by
• converting it to heat; that is how electric heaters work.
• The power dissipated by the resistor, measured in joules per second or
watts.

36. • The resistor and capacitor are in series.
• There are three voltmeters in the circuit and that the sum of their
readings must be zero:
• The voltage across the resistor,
• and the capacitor, are calculable via Ohm’s law
•
• Equation is a first-order differential equation

37. • Alternating Electricity: sine waves and square waves
• Alternating current electricity or ac
• The “alternating” designation indicates that the charge carriers
(electrons or ions) alternate in the direction in which they travel they
go backwards and forwards.
• The electricity that power utilities deliver to our homes and
laboratories is described either as “120 V a.c., 60 Hz” or “240 V a.c.,
50 Hz”
• The cited voltage, 120 V or 240 V, is the root-mean-square of the
continuously changing voltage, while the 60 or 50 designates the
frequency ῳ
• Frequency is expressed in the hertz

39. • A sine wave is a geometric waveform that oscillates (moves up,
down, or side-to-side) periodically,
• and is defined by the function y = sin x.
• In other words, it is an s-shaped, smooth wave that oscillates above
and below zero.

40. Square wave
• A periodic wave that varies abruptly in amplitude between two fixed
values, spending equal times at each.
• A square wave is a non-sinusoidal periodic waveform in which the
amplitude alternates at a steady frequency between fixed minimum
and maximum values, ..

41. sine waves and square waves
• Square wave inverters are usually used to support motors alone.
• Sine wave inverters are used to support household appliances such
as refrigerators ovens, computers, laptops, etc.
• Square wave inverters are less reliable and also unsafe to use for
appliances.
• Sine inverters are highly safe to use