UPSC Combined Geo-Scientist, Mains · 2020 · Mains Paper II
Q1(i). Electrochemical potential of zinc ions
Question
Are chemical and electrochemical potentials of aqueous Zn²⁺ the same? Give expressions.
Answer in brief
μ̃_(Zn²⁺)=μ_(Zn²⁺)+2Fφ=μ°+RTln a_(Zn²⁺)+2Fφ.
Key points
- Chemical potential measures the molar chemical contribution to Gibbs energy. For a species in solution, μᵢ=μᵢ°+RTln aᵢ.
- An ion also has electrostatic energy in the local electric potential φ. The molar electrochemical potential is μ̃ᵢ=μᵢ+zᵢFφ.
- For zinc zᵢ=+2, so the additional term is 2Fφ.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
CoversElectrochemical potential of zinc ionsElectrochemistry
All parts of Question 1
- 1(a) Critical-point inflection5 marks
- 1(b) Boyle and inversion temperatures5 marks
- 1(c) Accuracy at high diffraction angle5 marks
- 1(d) Composition change and non-expansion work5 marks
- 1(e) Van't Hoff plots5 marks
- 1(f) Potassium sulfate activities5 marks
- 1(g) Reaction order and rate constant5 marks
- 1(h) Catalytic rate enhancement5 marks
- 1(i) Electrochemical potential of zinc ions5 marks
- 1(j) Open-circuit emf and equilibrium5 marks
- 1(k) Hermitian operators5 marks
- 1(l) Probabilities of quantum states5 marks
- 1(m) Hydrogen rotational spectra5 marks
- 1(n) Wavelength and the einstein5 marks
- 1(o) Uranyl-sensitised decomposition5 marks
- 1(p) HI photolysis yield5 marks