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Edexcel IAL Chemistry 17.25 chelate stability and entropy

Use the substitution equation, not a vague stability claim: count particles before and after ligand exchange and link the positive ΔSsystem to feasibility.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
A2

Exam points

  • Count particles in ligand substitution equations to justify positive ΔSsystem.
  • Explain EDTA or salen stability through multidentate binding and entropy increase.
  • Compare ligand choices by the number of coordinate bonds and particles released.

17.25—Understand, in terms of the positive increase in ∆Ssystem, that the substitution of a monodentate ligand by a bidentate or question 1

[Maximum number: 2]

This question is about compounds and complex ions of iron.

Ethanedioate ligands react with iron(II) ions in aqueous solution.

[Fe(H2O)6]2++2C2O42−→[Fe(C2O4)2(H2O)2]2−+4H2O\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}+2 \mathrm{C}_{2} \mathrm{O}_{4}^{2-} \rightarrow\left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2-}+4 \mathrm{H}_{2} \mathrm{O}

Explain, in terms of entropy, why this reaction is feasible.

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