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3.2.14 electrode potentials and Gibbs energy changes (HL)

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chem whatarethemechanismsofchemicalchange

Reactivity 3.2.14 - the equation shows the relationship between standard change in Gibbs energy and standard cell potential for a reaction
electrode potentials and Gibbs energy changes both predict the directions of change
  • is related to the electrical energy when of charge passes through a circuit

considering a reaction where moles of electrons are transferred:

  • number of moles of electrons transferred in reaction
  • the charge carried by of electrons, known as the Faraday constant

a reaction is spontaneous when:

  • is positive
  • is negative
on interpreting data
  • both and give information on the energetic feasibility of a reaction
  • they do not give information on rate of reaction

if the activation is too high, a reaction predicted to be spontaneous may not happen at an observable rate

the values strictly apply to standard conditions, and changes in temperature, concentration, pressure will alter the values

the interpretation of electrode potential data involves that electrons always tend to flow towards the half-cell with the highest value

challenge questions
  1. determine a more precise value of the Faraday constant using information in the data booklet
  1. an equation that relates the Gibbs energy change of a reaction to its equilibrium constant is covered in reactivity 1.4. here we have used an equation that relates the Gibbs energy change to the electrode potential. formulate an equation to show how the potential of a cell depends on the equilibrium constant.
  1. identify a metal in section 19 of the data booklet which has a more negative electrode potential than expected from its reactivity with water and suggest an explanation for the discrepancy between its reactivity and its electrode potential

lithium has the most negative electrode potential, but is not the most reactive metal. the lower reactivity may be due to the slower rate of reaction. this might be linked to its relatively high melting point

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