Module 11: Electrochem

• Electrochemical cell


  a pair of electrodes in contact with an electrolyte solution.
• Cathode


  is an electrode where reduction occurs.
• Anode


  is an electrode where oxidation occurs.
• Galvanic Cells


  store electrical energy
• Electrolytic cells


  consume electricity and requires an external source of electrical energy for operation.
• Galvanic or Voltaic cell


  An electrochemical cell which spontaneously produces current (or energy) when the electrodes are connected externally by a conducting wire.
• Electrolysis or Electrolytic Cell


  an electrochemical cell through which current is forced by a battery or some other external source of energy.
• Half-cell reaction


  oxidation or reduction reaction occurring at an electrode.
• Anode (anox) - The electrode at which oxidation occurs.

  Cathode (redcath) - The electrode at which reduction occurs.
• Reversible Cell


  one in which the half-cell reactions are reversed by reversing the current flow; such a cell is said to be in thermodynamic equilibrium.
• Standard Hydrogen Electrode


  this consists of a platinum electrode coated with platinum black to catalyze the electrode reaction and over the surface of which hydrogen at 760 mm of mercury is passed.
• Electrode Potential E


  the potential of an electrode measured relative to a standard, usually the SHE. It is a measure of the driving force of the electrode reaction and is temperature and activity dependent.
• Standard Electrode Potential


  is measured in solutions where all reactants and products are at unit activity.
• Theoretical Cell Potential


  the algebraic sum of the individual electrode potentials of an electrochemical cell at zero current
• Liquid-junction potential


  a potential developed across a boundary between electrolytes differing in concentration or chemical composition.
• Ohmic Drop, IR


  the amount of potential that is lost on the way from the reference electrode to the working electrodes.
• Activation Overpotential


  the additional potential required to cause some electrode reactions to proceed at an appreciable rate.
• Concentration Overpotential

  the additional voltage that is needed to carry out electrolysis in addition to the standard cell potential.
• Oxidation


  is the loss of electrons in an atom.
• Reduction


  is the gain of electrons by an atom.
• Calomel Electrode


  the electrode consists of two concentric glass tubes, the inner one of which contains mercury in contact with a paste of mercury, mercuryl) chloride (calomel), and potassium chloride. Malria and yellow fever treatment.
• Silver-silver Chloride Electrode


  consists of a silver wire, coated with silver chloride and in contact with a solution of potassium chloride saturated with silver chloride.
• Calomel Electrode

  Disadvantage: slow to reach a new stable voltage following temperature change. Unstable above 80°C.
• Silver-silver Chloride Electrode

  Advantage: Can be used at high temperature up to 275°C.