Electrode Potentials and Electrochemical Cells

• how are electrochemical cells made?


  two different metals dipped in salt solutions of their own ions and connected by an external circuit
• why is the reaction redox?

  because one reaction is reduced and the other is oxidised
• what happens in the electrochemical cells?

  1. the element that loses electrons easily is oxidised and forms ions in the left half-cell. This releases electrons into the external circuit.
  2. in the other half-cell, the same number of electrons are taken from the external circuit, reducing the ions to atoms
• why is the salt bridge soaked in KNO3?

  it allows ions to flow through and balance out the charges
• which direction does electrons move in?

  electron flow through the wire from the more reactive metal to the less reactive metal
• what does the voltmeter in the external circuit show?

  shows voltage between two half-cells - cell potential
• why is the electrode platinum?

  because it is an inert metal, doesn't react with metal
• where does the conversion of charges happen?

  happens on the surface of a platinum electrode
• what does a negative electrode potential mean?

  means that a metal is easy to oxidise
• what does a positive electrode potential mean?

  means its harder to oxidise
• what is cell potential affected by?

  • temperature
  • concentration
  • pressure
• standard electrode potential?


  of a half-cell is the voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode
• standard conditions?


  • 100kPa
  • 298K(25 C)
  • 1.00 mol dm-3
• electrochemical series?


  a list of standard electrode potentials for different electrochemical half-cells
• what does more negative electrode potentials in half equations mean?

  1. right-hand side substances are more easily oxidised
  2. left-hand side substance are more stable
• what does more positive electrode potentials in half equations mean?

  1. left-hand side substances are more easily reduced
  2. right-hand side substance are more stable
• how to calculate E°cell?

  E°reduced - E°oxidised
• how is rechargeable batteries recharged?

  a current is supplied to force electrons to flow in opposite direction around the circuit and reverse the reaction.
• where are the chemicals stored in a fuel cell?

  stored separately outside the cell and fed in then electricity is required
• what are the disadvantages of fuel cells?

  • energy needed to produce a supply a hydrogen and oxygen, they can be produced from electrolysis of water
  • reusing waste products from fuel cells requires electricity but electricity is generated by burning fossil fuels - not carbon neutral
  • hydrogen is highly flammable - need to be stored/transported carefully
• what are the disadvantages of fuel cells?

  • efficient: they convert more of their available energy into kinetic energy in cars. internal combustions engines waste energy producing heat
  • water is the only waste product -no toxic chemicals + no C02 emissions
  • doesn't need to be recharged. as long as hydrogen and oxygen are supplied, cell will continue to produce electricity