electrochemistry

• In galvanic cell:

  • polarity of anode: negative
  • polarity of cathode: positive
• standard electrode potential: relative potential of this electrode under standard conditions compared to the standard hydrogen electrode whose electrode potential is assigned 0V at 298K
• standard hydrogen electrode: hydrogen gas at 1 bar bubbling over platinum electrode coated with finely divide platinum dipped in 1 moldm-3 H+(aq)
• Gibbs free energy G=-nFEcell

  • n = number of electrons per mole reaction
  • F = 96500
• in electrolytic cell:

  • polarity of anode: positive, attached to positive terminal of battery, attracts anions
  • polarity of cathode: negative, attached to negative terminal of battery, attracts cations
• Q (quantity of charge) = I (current) x t (time/s)
• Q (quantity of charge) = n (amount of electrons) x F (96500)

  
  

  Q = n x Le

  L (Avogadro’s constant, 6.02 x 10^23)

  e (charge on 1 electron, 1.60 x 10^-19)
• purpose of anodising aluminium: aluminium is readily oxidised by oxygen in air, anodising allows for formation of thick and uniform layer of aluminium oxide on surface, makes aluminium resistant to corrosion
• Anodising aluminium:

  • at anode: 2Al + 3H2O -> Al2O3 + 6H+ +6e
  • at cathode: 2H+ +2e -> H2