CIE A Level Chemistry

Revision Notes

Syllabus Edition

First teaching 2020

Last exams 2024

|

6.3.2 Predicting Feasibility of Redox Reactions

Test Yourself

Feasibility of Redox Reactions Using Standard Electrode Values

  • Transition elements can form ions with various oxidation states
  • The change in their oxidation states involves the transfer of electrons
  • Transition elements are often involved in redox reactions
  • A redox reaction is a reaction in which one species is oxidised (loses electrons) and another is reduced (gains electrons)
  • The standard electrode potentials (E) of the two species can be used to predict the feasibility of redox reactions involving transition elements and their ions

Predicting feasibility of redox reactions

  • The standard electrode potential (E) of a species gives an indication of how well it can be reduced
  • In the exam, you will be provided with a half equation and the standard electrode potential (E)
  • The half equations are always written as a reduction equation
    • They are equilibrium reactions, as they demonstrate the equilibrium reached when the species in the equation gains electrons at the same rate as it is losing electrons

  • The more positive the standard electrode potential (E) of a species is, the more readily that element will be reduced (gain electrons)
    • This is always when compared to the standard hydrogen electrode
    • The opposite is of course true; the more negative the standard electrode potential (E) of a species is, the more readily that element will be oxidised (lose electrons)

  • The feasibility of a reaction can be predicted using these values
  • For example, the feasibility of Fe3+ being reduced to Fe2+ when reacted with Cu2+, can be predicted using their standard electrode potentials

Standard electrode potentials of Fe(III) & Cu(II) table

Chemistry of Transition Elements - Standard electrode potentials of Fe(III) and Cu(II) table, downloadable AS & A Level Chemistry revision notes

  • The table above shows that yes, the reaction is feasible and Fe3+ is more likely to get reduced to Fe2+
    • Fe3+ has a more positive standard electrode potential
    • Fe3+ will gain electrons more readily than Cu2+
    • Therefore, Fe3+ is the better oxidising agent
    • The reaction for this half equation will therefore proceed in the forward direction (reduction)

  • Since it is feasible that the Fe3+ will be reduced and this half equation will move in the forward direction, this means that the half equation for copper will move in the backward direction (oxidation)
    • Cu2+ equation has a less positive (or more negative) standard electrode potential
    • The Cu+ will therefore be oxidised to Cu2+
    • The reaction for this half equation will therefore be in the reverse direction

  • Combining these two half-equations to get the overall equation gives (after cancelling the electrons on both sides):

Feasibility of Redox Reactions Using Standard Electrode Values equations

  • The positive value of Ecell (+0.62 V) suggests that the reaction is likely to proceed
  • The changes in the transition element ions’ oxidation states are therefore feasible
  • Standard electrode potentials (E) are only predictions about the feasibility of a reaction; they do not guarantee that a reaction will definitely occur
    • For example, a reaction may be feasible according to these rules, but have a very large activation energy barrier meaning that in reality it will not occur

You've read 0 of your 0 free revision notes

Get unlimited access

to absolutely everything:

  • Downloadable PDFs
  • Unlimited Revision Notes
  • Topic Questions
  • Past Papers
  • Model Answers
  • Videos (Maths and Science)

Join the 80,663 Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Francesca

Author: Francesca

Fran studied for a BSc in Chemistry with Forensic Science, and since graduating taught A level Chemistry in the UK for over 11 years. She studied for an MBA in Senior Leadership, and has held a number of roles during her time in Education, including Head of Chemistry, Head of Science and most recently as an Assistant Headteacher. In this role, she used her passion for education to drive improvement and success for staff and students across a number of subjects in addition to Science, supporting them to achieve their full potential. Fran has co-written Science textbooks, delivered CPD for teachers, and worked as an examiner for a number of UK exam boards.