What is the standard Gibbs energy for the reaction?Zn (s) + Cu2+ (aq)…

The correct answer is Option (1) → − 212.27 kJ mol⁻¹

A galvanic cell does electrical work at the cost of the reaction’s Gibbs energy. For n moles of electrons passing through a cell of standard emf E°_cell:

    \( \displaystyle \Delta_rG^{\circ}=-nFE^{\circ}_{cell} \)

A positive E°_cell gives a negative ΔG°, which means the cell reaction is spontaneous.

For the Daniell cell:

    \( \displaystyle \ce{Zn(s) + Cu^2+(aq) -> Zn^2+(aq) + Cu(s)} \)

• Anode: \( \ce{Zn(s) -> Zn^2+(aq) + 2e^-} \); cathode: \( \ce{Cu^2+(aq) + 2e^- -> Cu(s)} \); so n = 2.

• E°_cell = E°_cathode − E°_anode = 0.34 − (−0.76) = 1.10 V.

    \( \displaystyle \Delta_rG^{\circ}=-2\times96487\ \mathrm{C\,mol^{-1}}\times1.10\ \mathrm{V} \)

    \( \displaystyle \Delta_rG^{\circ}=-212271\ \mathrm{J\,mol^{-1}} \)

    \( \displaystyle \Delta_rG^{\circ}=-212.27\ \mathrm{kJ\,mol^{-1}} \)

Shortcut: 2 × 96500 × 1.1 ≈ 212000 J, which is about 212 kJ, and the sign must be negative for a working cell. Only Option (1) fits.

Note 1: In the book’s working (extract below), the value in joules is printed as −21227 J mol⁻¹; it should be −212270 J mol⁻¹, which is the −212.27 kJ mol⁻¹ given on the next line.

Note 2: This question is from NCERT (2026-27). NTA sets numerical questions from NCERT too, so do not ignore NCERT while practising numericals.

NCERT (2026-27 edition):
Electrochemical Cell and Gibbs Energy of the Reaction – …

Note 3: The same/similar question has been asked in different years by NTA as per the details given below: