Predictions from electrode potentials

• Predictions can be made about the feasibility of any potential redox reactions using standard electrode potentials
• • The most negative system has the greatest tendency to be oxidised and lose electrons
• • The most positive system has the greatest tendency to be reduced and gain electrons
• An oxidising agent takes electrons away from the species being oxidised. So oxidising agents are reduced and are on the left.
• A reducing agent adds electrons to the species being reduced. So reducing agents are oxidised and are on the right
• You can predict the feasibility of redox reactions from E values
• • The strongest reducing agent is at the top on the right
  • The strongest oxidising agent is at the bottom on the left
• △G = -nFE cell

  • n = moles of electrons transferred in the balanced equation
  • F is the Faraday constant = 96,500 C mol-1
• E cell = E (positive electrode) - E (negative electrode)
• Providing that E cell is positive, △G will be negative. The smaller value of E cell, the less negative the value of △G
• △G is the free energy change / the overall change in energy during a chemical reaction
• A small negative value of △G suggest that the feasibility may be susceptible to small changes in conditions
• Limitations for predictions of feasibility based on E values

  • The reaction may have a slow rate with high activation energy
  • The concentration may not be 1 mol dm-3 changing the E value
• In an electrochemical series

  • the equilibrium with the more negative electrode potential will go towards the electrons
  • the equilibrium with the more positive electrode potential will go away from the electrons
• When adding the half equations to give the overall equation, we need the same number of electrons on each side