- 2068 Bhadra · 1+4 marks
Galvanic vs electrolytic cell; Cd/Cu cell emf
Short answer
Galvanic cells generate electricity from spontaneous reactions; electrolytic cells consume electricity for non-spontaneous ones. The Cd–Cu cell EMF: E°cell = 0.48 V, using Nernst equation E = 0.48 − (0.0591/2) log(0.01/0.5) = 0.53 V.
How does a galvanic cell differ from an electrolytic cell? Calculate the emf of the following cell at 25°C giving electrode reactions and cell reaction. Cd(s)|Cd²⁺(0.01M)//Cu²⁺(0.5M)|Cu(s) E°Cd²⁺/Cd = −0.140 V, E°Cu²⁺/Cu = 0.34 V
Galvanic cell vs electrolytic cell
| Point | Galvanic cell | Electrolytic cell |
|---|---|---|
| Energy change | Chemical → electrical | Electrical → chemical |
| Reaction | Spontaneous | Non-spontaneous (driven by external source) |
| Anode | Negative | Positive |
| Cathode | Positive | Negative |
| Salt bridge | Needed (two half cells) | Not needed (one cell) |
| Example | Daniell cell | Electrolysis of fused NaCl |
EMF of Cd | Cd²⁺ (0.01 M) || Cu²⁺ (0.5 M) | Cu
Anode : Cd → Cd²⁺ + 2e⁻
Cathode : Cu²⁺ + 2e⁻ → Cu
Cell : Cd + Cu²⁺ → Cd²⁺ + Cu (n = 2)
E°cell = E°(Cu²⁺/Cu) − E°(Cd²⁺/Cd) = 0.34 − (−0.140) = 0.48 V
Q = [Cd²⁺]/[Cu²⁺] = 0.01/0.5 = 0.02 , log Q = −1.699
E = E° − (0.0591/2) log Q
= 0.48 + 0.02955 × 1.699
= 0.48 + 0.0502 = 0.530 V
Answer: EMF ≈ 0.53 V (E°Cd as given in the question).
✓ Answer checked by Claude Opus 5.5 (high effort)
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