electrode potentials and cells

• What type of reactions do electrochemical cells use?


  Redox reactions
• What is created by the electron transfer in electrochemical cells?


  A flow of electrons
• What does the flow of charged particles in an electrochemical cell represent?


  An electrical current
• What is produced between the two electrodes in an electrochemical cell?


  A potential difference
• What are the main components of most electrochemical cells?


  • Two solutions with metal electrodes
  • A salt bridge
• What is the function of a salt bridge in an electrochemical cell?


  To carry the flow of charge without interfering with the reaction
• What is each solution in an electrochemical cell called?


  A half-cell
• What does the cell potential of a half-cell indicate?


  How it will react, either as an oxidation or reduction reaction
• What are the specific rules for conventional cell representation?


  • The half-cell with the most negative potential goes on the left
  • The most oxidised species goes next to the salt bridge
  • A salt bridge is shown using a double line
  • Always include state symbols
• What is the cell potential of the standard hydrogen electrode (SHE)?


  0.00V
• Under what conditions is the standard hydrogen electrode measured?


  Under standard conditions
• What are the standard conditions for measuring the SHE?


  • Solutions of 1.0 moldm^-3 concentration
  • A temperature of 298K
  • 100 kPa pressure
• What materials are used in the standard hydrogen electrode?


  Hydrochloric acid, hydrogen gas, and platinum electrodes
• Why are platinum electrodes used in the standard hydrogen electrode?


  They are metallic and inert
• How are cell potentials measured under standard conditions?


  Compared to the SHE
• What does a negative cell potential indicate about a substance?

  It is more easily oxidised and will lose electrons
• What does a positive cell potential indicate about a substance?

  It is more easily reduced and will gain electrons
• How is the overall cell EMF calculated?


  • Potential of the right of the cell minus the potential of the left
  • Most positive potential minus the most negative potential
• What does a positive overall cell potential indicate about the reaction?

  The reaction is spontaneous and favourable
• How does the value of cell potential relate to the favourability of a reaction?


  The more positive the potential, the more favourable the reaction
• What is the anticlockwise rule for combining half-cell reactions?


  1. Write the most negative EMF on top
  2. Draw anticlockwise arrows around the reactions
  3. Balance the electrons on both sides
  4. Write out the cell reaction
• What type of agents are substances with very positive electrode potentials?


  Better oxidising agents
• What type of agents are substances with very negative electrode potentials?


  Better reducing agents
• What effect does increasing the concentration of solutions have on cell EMF?


  It makes the cell EMF more positive
• What effect does increasing the pressure of the cell have on cell EMF?


  It makes the cell EMF more negative
• What types of electrochemical cells are used commercially?


  • Non-rechargeable cells
  • Rechargeable cells
  • Fuel cells
• What characterizes a rechargeable cell?


  The reaction is reversible, allowing the cell to be reformed
• What is a common type of rechargeable battery?

  Lithium ion cells
• What electrodes are used in lithium ion cells?

  Lithium Cobalt Oxide and Graphite electrodes
• What is used as an electrolyte in lithium ion cells?


  A lithium salt in an organic solvent
• How is a rechargeable cell recharged?


  • A current is applied over the cell
  • Electrons move in the opposite direction
  • The reaction reverses, recharging the cell
• What distinguishes non-rechargeable cells from rechargeable cells?


  Non-rechargeable cells have irreversible reactions
• What is a fuel cell?


  • Generates electrical current without needing to be recharged
  • Uses a continuous supply of reactants
• What is the most common type of fuel cell?


  Hydrogen fuel cell
• What does a hydrogen fuel cell use to generate a continuous current?


  A continuous supply of Hydrogen and Oxygen from air
• What is the only waste product of the reaction in a hydrogen fuel cell?


  Water
• Why are hydrogen fuel cells considered environmentally friendly?


  They produce water as the only waste product
• What are some downsides to hydrogen fuel cells?


  High flammability of Hydrogen and expensive to produce