Electrochemistry

• Alkaline hydrogen - oxygen fuel cell

  Half equations:

  • electrodes are separated by a semi permable membrane
  • electrodes made of a porous platinum based material
  • the electrolyte is sodium hydroxide solution
  • used to generate electricity as the only by product is water so it is very environmentally safe to use

  
• SHE

  Standard hydrogen electrode

  • 298K
  • 100kPa
  • 1moldm-3
  • An inert electrode, typically platinum

  Standard electrode potential value of 0V

  
• Representing cells

  The more positive electrode potential goes on the right hand side.

  The process is R O O R.

  Salt bridge - potassium nitrate... allows ions to flow through the solution.

  
• NON RECHARGEABLE CELLS

  Zinc- copper

  • Daniell Cell
  • Low toxic waste
  • Cheap
  • Non rechargeable
  • EMF of 1.1V
  • Initially used to provide electricity for old fashioned telegraphs
• NON RECHARGEABLE CELLS

  Zinc- carbon cell

  
• RECHARGEABLE BATTERY

  The recharge occurs by reversing the cell reaction.

  • done by appling an external voltage > voltage of the cell to drive the electrons in the opposite direction
• Lead acid battery

  • Rechargeable
  • Used in cars
  • Positive plate made of lead coated with lead (IV) oxide and the negative plate is made of lead
• Portable battery

  Nickel/cadmium cell

  • replace zinc carbon batteries
  • expensive
  • can be recharged up to 500 times
• Lithium ion

  • Used in laptops, tablets, smartphones and other gadgets
  • Light because lithiumi s the leastdense metal
  • Electrons flow from -ve to +ve
• NO PROBLEM

  • negative electrode potential value is oxidation
  • positive electrode potential value is reduction
• Ecell


  E cell = E reduction - E oxidation