Electrode potentials and electrochemical cells

• A salt bridge is a tube of unreactive ions that can move between the solutions to carry the flow of charge
• Conventional cell representation

  The half-cell with the most negative potential goes on the left

  The species with the highest oxidation state from each half-cell goes next to the salt bridge

  A salt bridge is shown using a double line

  Always include state symbols
• The standard hydrogen electrode (SHE) is the measuring standard for half-cell potentials. It has a cell potential of 0.00V under standard conditions
• Standard conditions

  • concentration: 1.0 moldm-3
  • temperature: 298K
  • pressure: 100kPa
• Platinum electrodes are used when there are no solid electrodes in the half cell. They are metallic, so will conduct electricity, but are also inert so will not interfere with the reaction
• Negative potentials mean the substances are more easily oxidised and will lose electrons to become more stable.

  Positive potentials mean the substances are more easily reduced and will gain electrons to become more stable.
• Electromotive force (EMF) of a cell is the potential of the right cell minus the potential of the left cell
• The more positive the overall cell potential value is, the more spontaneous and favourable the reaction.
• More positive electrode potentials are better oxidising agents and will oxidise species more negative than it.

  More negative electrode potentials are better reducing agents and will reduce species less negative than it.
• The disadvantages of hydrogen fuel cells: hydrogen is highly flammable and expensive to produce