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NEET Chemistry · Redox Reactions and Electrochemistry

Nernst equation and Gibbs energy

Taught in NCERT Class 12 Chemistry, Chapter 2: Electrochemistry.

2 verified questions: Easy 0 · Medium 1 · NEET level 1

Sample questions

Sample 1Medium

For the cell Zn(s) | Zn^2+(0.1 M) || Cu^2+(1.0 M) | Cu(s), E°cell = 1.10 V at 298 K. What is the cell potential? (Take 2.303RT/F = 0.059 V)

  1. A

    1.07 V

  2. B

    1.10 V

  3. C

    1.04 V

  4. D

    1.13 V

Show the answer
The answer is D.

E = E° − (0.059/2) log([Zn^2+]/[Cu^2+]) = 1.10 − 0.0295 × log(0.1) = 1.10 + 0.0295 ≈ 1.13 V.

  • A.

    This subtracts the correction; with [Zn^2+] < [Cu^2+] the log term is negative, so E rises above E°.

  • B.

    E equals E° only when the concentration ratio is 1.

  • C.

    This uses n = 1 and the wrong sign, both errors.

NCERT: Class 12 Chemistry, Chapter 2, 2.3

Sample 2NEET level

For the Daniell cell, Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s), the standard cell emf is 1.1 V. Taking F = 96487 C mol⁻¹, the standard Gibbs energy of the reaction is

  1. A

    −106.1 kJ mol⁻¹

  2. B

    +212.3 kJ mol⁻¹

  3. C

    −424.5 kJ mol⁻¹

  4. D

    −212.3 kJ mol⁻¹

Show the answer
The answer is D.

ΔrG° = −nFE°cell, with n = 2 for this reaction. ΔrG° = −2 × 96487 C mol⁻¹ × 1.1 V = −212271 J mol⁻¹ ≈ −212.3 kJ mol⁻¹.

  • A.

    Uses n = 1 instead of n = 2.

  • B.

    Wrong sign: a positive emf gives a negative ΔrG°.

  • C.

    Uses n = 4 instead of n = 2.

NCERT: Class 12 Chemistry, Unit 2 (Electrochemistry), Electrochemical Cell and Gibbs Energy of the Reaction

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