Electrode Potentials

Electrode Potentials

1. Electrochemical cells

   • You need 2 different metal electrodes.
     • These shOuld be dipped in a salt solution of the same ions.
       • Since this is a redox reaction, electricity can be made.
         • The more reactive of the two metals will get oxidized.
           • The e-'s that are released travel through to the other solution.
             • These e-'s then reduce the ions in the solution.
   • The salt bridge
     • This is used to allow ions to flow between the 2 half cells.
       • It balances out the charges.
       • It completes the circuit.

2. Electromotive force (EMF)

   • EMF is the potential difference between the 2 half-cells.
     • It is measured by attaching a voltmeter to the cell.
       • This is obviously measured in Volts.
         • The higher the difference, the greater the reactivity difference
           • The EMF also tells you if the reaction is feasible
             • If EMF is +ve, the reaction is feasible
               • EMF = Reduction - Oxidation

3. Potentials

   • If it's an oxidation reaction, the Ep will be more -ve.
     • Ep means electrode potential
     • The higher the negativity, the stronger the reducing agent.
   • If it's a reduction reaction, Ep will be more +ve.
     • This means the metal is less reactive

4. Diagrams

   • The conventional representation

5. The standard H2 electrode

   • The standard conditions
     • 1moldm-3 conc.
     • 298K
     • 100kPa
   • This half cell is always 0V.
     • So it can be used measure the Ep of metals

6. Batteries

   • re-chargeable
     • E.g. LiCOo2 ELECTRODE AND graphite. The electrolyte is a Li salt in a organic solvent.
     • Uses a reversible reaction.
       • Lasts longer
         • Laptops
   • Non-rechargeable
     • The opposite.

7. Fuel cells

   • Used to power cars.
     • It uses up all the available energy so less is wasted.
   • The Hydrogen-oxygen fuel cell
     • Hydrogen is supplied at the -ve electrode.
       • H2 + 2OH- ----- 2H2O + 2e-
       • Oxygen is at the positive electrode.
         • O2 + 2H2O + 4e- -----  4OH-
         • These gasses are continuously fed in to keep the reaction going.
           • There are also anion membranes to allow only the OH- ions through,
             • This acts as the electrolyte
               • The overall reaction, 2H2 + O2 ----- 2H2O

Imagens e arquivos do mapa