Online Notes on "Electrochemistry" (Chapter=>3 ) Part 2

These are Online Notes on "Electrochemistry" (Chapter=>3 ) Part 2 for practice of CBSE BOARD, CBSE NEET, CSIR NET Chemical Sciences etc.

25. The potential difference between the 2 electrodes of a galvanic

cell is called cell potential and is measured in Volts.

26. The cell potential is the difference between the reduction

potential of cathode and anode.

E_cell = E_cathode – E_anode

Cell potential is called the electromotive force of the cell (EMF) when no

current is drawn through the cell.

27. Nernst studied the variation of electrode potential of an

electrode with temperature and concentration of electrolyte.

28. Nernst formulated a relationship between standard electrode

potential E^o and electrode potential E.

E =  E^o - [ ( 2.303 RT ) / nF ]  log { 1 / [Mⁿ⁺] }

E =  E^o -  [ ( 0.059 ) / nF ]  log { 1 / [Mⁿ⁺] }             (at 298K)

29. Electrode potential increases with increase in the concentration of the electrolyte and decrease in temperature.

30. Nernst equation when applied to a cell:

E =  E^o -  [ ( 2.303 RT ) / nF ]  log { [Anode ion] / [Cathode ion] }    

31. At equilibrium, cell potential E_cell becomes zero.

32. Relationship between equilibrium constant K_c and standard cell

potential E^o cell :

E =  [ ( 0.059 ) / nF ]  log K_c   (at 298)

33. Work done by an electrochemical cell is equal to the decrease in Gibbs

energy

ΔG^o = -nFE^o_cell

34. The substances which allow the passage of electricity through

them are known as conductors.

35. Every conducting material offers some obstruction to the flow of

electricity which is called resistance. It is denoted by R and is measured in

ohm.

36. The resistance of any object is directly proportional to its length l and inversely proportional to its area of cross section A.

R = ρ ( l / A )

ρ is called specific resistance or resistivity. Its SI unit is ohm metre.

37. The inverse of resistance is known as conductance, G

Unit of conductance is ohm-1 or mho. It is also expressed in Siemens

denoted by S.

G = 1 / R

38. The inverse of resistivity is known as conductivity. It is

represented by the symbol  κ. The SI unit of conductivity is Sm-1. But it is

also expressed in S cm-1

 κ = 1 / ρ = 1/R (l/A) = G (l/A)

So, conductivity = Conductance × Cell constant

39. For measuring the resistance of an ionic solution, there are 2

problems:

a) Firstly, passing direct current changes the composition of the solution

b) Secondly, a solution cannot be connected to the bridge like a metallic

wire or a solid conductor.

40. This can be resolved by using a source of alternating current and the

second problem is resolved by using a specially designed vessel called

conductivity cell.
Click HERE for Online Notes on "Electrochemistry" (Chapter=>3 ) Part 3