BRANCH OF PHYSICAL CHEMISTRY THAT STUDIES THE INTERRELATIONSHIP BETWEEN ELECTRICITY AND CHEMISTRY

1. ELECTROCHEMISTRY BRANCH OF PHYSICAL CHEMISTRY THAT STUDIES THE INTERRELATIONSHIP BETWEEN ELECTRICITY AND CHEMISTRY

2. THE SUBSTANCES WHICH ALLOW ELECTRIC CURRENT THROUGH THEM ARE CONDUTORS THESE ARE OF TWO TYPES.METALLIC OR ELECTRONIC CONDUTORS EX: COPPER METALELECTROLYTIC CONDUCTORS OR ELECTROLYTES EX: Nacl solution, acids

3. Electrolytes Substances whose solution in water conducts electric current. Conduction takes place by the movement of ions. Examples are salts, acids and bases. Substances whose aqueous solution does not conduct electricity are called non electrolytes. Examples are solutions of cane sugar, glucose, urea etc.

4. OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen. REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen. OXIDIZING AGENT—electron acceptor; species is reduced. REDUCING AGENT—electron donor; species is oxidized. Terminology for Redox reactions

5. Oxidation and Reduction Oxidation and Reduction • A species is oxidized when it loses electrons. – Here, zinc loses two electrons to go from neutral zinc metal to the Zn2+ ion. – Oxidation is observed as an increase in oxidation number

6. Oxidation and Reduction • A species is reduced when it gains electrons. • A species is oxidized when it loses electrons.

7. Specific conductance:is the conductance shown by a cell of 1 unit length and 1 unit area of cross section containing electrolyte. CGS units are Ohm-1 cm-1 SI units of siemens per meter (S·m-1)

8. Molar conductance It is the conductance of a solution containing 1 mole of the electrolyte in V cc of solution. it is represented as m. ex: 98 g of sulfuric acid in one liter of water. =k x 1000/M Where V = volume solution in cc m = Molar conductance k = Specific conductance M=molarity of the solution.

9. Mathematically, Equivalent Conductance It is the conductance of one gram equivalent of the electrolyte dissolved in V cc of the solution. Equivalent conductance is represented by ex: 49 g of sulfuric acid in one liter of water. Where, k = Specific conductivity V = Volume of solution in cc. containing one gram equivalent of the electrolyte.

10. EFFECT OF DILUTION ON CONDUCTANCE Specific conductivity decreases on dilution. Equivalent and molar conductance both increase with dilution and reaches a maximum value. The conductance of all electrolytes increases with temperature.

11. Some important laws: Ohms law for metallic conductors: I=E/R I=Current flowing through conductor, E= electromotive force, R=resistanceSpecific conductance =R* S/L equivalent conductance = K*1000 Nmolecular conductance = K*1000 M

12. CHEMICAL CHANGE --->ELECTRIC CURRENT • To obtain a useful current, we separate the oxidizing and reducing agents so that electron transfer occurs through an external wire.

13. Line Notation • solid½Aqueous½½Aqueous½solid • Anode on the left½½Cathode on the right • Single line different phases. • Double line porous disk or salt bridge. • If all the substances on one side are aqueous, a platinum electrode is indicated.

14. CELL POTENTIAL, E • For Zn/Cu cell, potential is +1.10 V at 25 ˚C and when [Zn2+] and [Cu2+] = 1.0 M. • This is the STANDARD CELL POTENTIAL, Eo • —a quantitative measure of the tendency of reactants to proceed to products when all are in their standard states at 25 ˚C.

15. Zn --> Zn2+ + 2e- Cu2+ + 2e- --> Cu Oxidation Anode Negative Reduction Cathode Positive •Electrons travel thru external wire. • Salt bridge allows anions and cations to move between electrode compartments. <--Anions Cations--> RED CAT

16. ELECTROMOTIVE FORCE is "that which tends to cause current (actual electrons and ions) to flow. Nernst equation is an equation that can be used to determine the equilibrium reduction potential of a half-cell in an electrochemical cell. It can also be used to determine the total voltage (electromotive force) for a full electrochemical cell.

17. Calculating Cell Voltage • Balanced half-reactions can be added together to get overall, balanced equation. Zn(s) ---> Zn2+(aq) + 2e- Cu2+(aq) + 2e- ---> Cu(s) -------------------------------------------- Cu2+(aq) + Zn(s) ---> Zn2+(aq) + Cu(s) If we know Eo for each half-reaction, we could get Eo for net reaction.

19. A Concentration cell is an electrochemical cell that has two equivalent half-cells of the same material differing only in concentrations

20. A Reference electrode is an electrode which has a stable and well-known electrode potential. Some reference electrodes areStandard Hydrogen electrode Saturated calomel electrode glass electrode

21. STANDARD HYDROGEN ELECTRODE This is represented as Pt, H2 / H+   760 mm of Hg) (IM) Platinum foil is immersed in standard 1M solution of HCl and H2 gas is bubbled with I atm pressure.

22. GLASS ELECTRODE EXAMPLE OF ION SELECTIVE ELECTRODE H+ from solution diffuse into the membrane. Response of glass electrode (at 25 °C):

23. BATTERIES AND FUEL CELLSBatteries are classified into two types. Primary batteries non rechargeable batteries.Secondary or rechargeable batteries.

24. When two electrochemical cells are interconnected which are containing electrodes and electrolytes called as battery.

25. PRIMARY BATTERIES • Dry Cell or Leclanche or Zinc-carbon cell

26. Dry cell Zn + NH4 Cl+ ZnCl2+MnO2 ® Zn(NH3 )2 Cl2 + 2H2O + Mn2O3 In dry cell Zn is anode and cathode is MnO2 and the electrolyte is 26%NH4Cl, 8.8%ZnCl2 & 65.2%H2O and the following reaction takes place

27. Alkaline Battery Nearly same reactions as in common dry cell, but under basic conditions. Anode (-): Zn + 2 OH- ---> ZnO + H2O + 2e- Cathode (+): 2 MnO2 + H2O + 2e- ---> Mn2O3 + 2 OH-

28. In Some primary batteries mostly Lithium is used as anode

29. Liquid cathode lithium cells(Li-Socl2)solid cathode lithium cells(Li-MnO2)Solid electrolyte lithium cells(Li-P2VP)These lithium cells have high voltage3to 3.5 volts and run for long time.

30. Secondary Batteries • Secondary batteries are rechargeable and reusable. • Ni-Cd cell: • anode: Cd • Cathode: NiO2 • Electrolyte: aq.KOH • NiO2 + Cd + 2H2O ®Cd(OH)2 +Ni(OH)2

31. During discharging reaction of nicd cell is NiO2 + Cd + 2H2O ®Cd(OH)2 +Ni(OH)2during recharging reaction of nicd cell isCd(OH)2 +Ni(OH)2 NiO2 + Cd + 2H2O

33. Secondary batteries • Car batteries are lead storage batteries. • It consists or 12 lead acid voltaic cells. • Spongy lead is anode • PbO2 is cathode. • Sulphuric acid is electrolyte. • Each pair of anode cathode generates 2volts.

34. During discharging equation is • Pb +PbO2 +2H2SO4 2PbSO4(s) +2H2O • During recharging equation is • 2PbSO4(s) +2H2O Pb+PbO2 +2H2SO4 • During discharging secondary batteries act as electrochemical cells • And during recharging acts as electrolytic cells.

35. Lithium ion cell

36. A lithium-ion battery is a member of family of rechargeable battery types in which lithium ions move from the anode to the cathode during discharge and back when charging. Li-ion batteries use an intercalated lithium compound as the electrode material anode-graphite cathode LiCoO2 electrolyteLiBF6

38. FUEL CELLS FUELS ARE CONTINUOUSLY SUPPLED FROM EXTERNAL TO THE CELL.THE HYDROGEN OXYGEN FUEL CELS ARE CLASSIFIED AS FOLLOWS Proton Exchange Membrane fuel cells. Alkaline fuel cells Molten Carbonate fuel cells Phosphoric acid fuel cells Solid oxide fuel cells.

39. H2 as a Fuel Cars can use electricity generated by H2/O2 fuel cells. H2 carried in tanks or generated from hydrocarbons

41. The End