Electrochemical Cells

• Difference between galvanic (voltaic) and electrolytic cells.
• Anode (oxidation) and cathode (reduction); electron flow and ion migration in salt bridge.
• Standard cell notation: Zn|Zn²⁺||Cu²⁺|Cu and calculating EMF E°cell = E°cathode − E°anode.
• Electrolysis — Faraday's laws linking charge, moles, and mass deposited.
• Commercial cells: dry cell, lead storage battery, fuel cell (NCERT overview).

Level 1 — Foundations

Verbal: Electrochemical cells convert chemical energy to electrical (galvanic) or use electricity to drive non-spontaneous reactions (electrolytic).

Galvanic cell: Spontaneous redox; anode (−) oxidation; cathode (+) reduction; electrons external wire anode → cathode.

Salt bridge: Maintains neutrality via ion flow; completes circuit.

Standard electrode potential E°: Measured vs SHE (H⁺/H₂, E° = 0).

Cell EMF: E°cell = E°cathode − E°anode ( reduction − oxidation potentials).

Level 2 — JEE / NEET depth

Daniel cell: Zn → Zn²⁺ + 2e⁻ (anode); Cu²⁺ + 2e⁻ → Cu (cathode); E°cell ≈ 1.10 V.

Spontaneity: ΔG° = −nFE°cell. If E°cell > 0, spontaneous as written.

Electrolytic cell: External battery forces reverse; anode becomes positive terminal (oxidation still at anode by definition).

Faraday's 1st law: m ∝ Q = It. 2nd law: Same Q deposits moles proportional to equivalent weight.

Faraday constant: F ≈ 96500 C/mol e⁻.

Overpotential: Extra voltage beyond E° to overcome kinetic barriers — qualitative in NEET.

EMF of Daniell cell

E°(Zn²⁺/Zn) = −0.76 V, E°(Cu²⁺/Cu) = +0.34 V.

Step 1 — Cathode (reduction): Cu²⁺/Cu (+0.34 V).
Step 2 — Anode (oxidation): Zn/Zn²⁺ (−0.76 V).
Step 3 — E°cell = 0.34 − (−0.76) = 1.10 V.
Step 4 — Spontaneous; ΔG° = −2 × 96500 × 1.10 J/mol negative.

Electrolysis copper deposition

Current 2 A for 965 s through Cu²⁺ solution. Mass deposited?

Step 1 — Q = It = 2 × 965 = 1930 C.
Step 2 — Moles e⁻ = Q/F = 1930/96500 = 0.02 mol.
Step 3 — Cu²⁺ + 2e⁻ → Cu: moles Cu = 0.01 mol.
Step 4 — Mass = 0.01 × 63.5 = 0.635 g.

• Define anode and cathode in galvanic cell.
• Write Daniell cell cell reaction.
• State Faraday's first law.
• E°cell = −0.5 V — spontaneous as written?
• Stretch: Calculate time to deposit 1 g Ag with given current.

NCERT Chapter 3 link: Electrochemical cells split into galvanic (spontaneous) and electrolytic (driven). Anode is oxidation regardless of sign — definition by process not polarity alone in galvanic cells.

Exam connections: Calculate E°cell from standard electrode potentials — cathode minus anode. Faraday's laws link charge to mass deposited — n = Q/F for moles of electrons. ΔG° = −nFE°cell connects thermodynamics to electrochemistry.

Study strategy: Cell notation: anode | anode electrolyte || cathode electrolyte | cathode. Salt bridge prevents charge accumulation. For electrolysis, identify products at each electrode using discharge series.

When studying Electrochemical Cells within Electrochemistry, start by listing every formula and definition on one page without looking at the textbook. Compare your list to NCERT — missing items indicate gaps to fix immediately. Work through at least two NCERT Examples for this section with steps written in full; examiners award method marks even when arithmetic slips.

For board exams (CBSE), long answers benefit from a clear structure: definition → explanation → diagram or formula → example → brief conclusion. Underline key terms. For JEE Main and NEET, prioritise conceptual traps and quick calculation paths; timed mixed quizzes of 10 questions after revision simulate exam pressure.

Cross-topic link: Stoichiometry from Class 11 mole concept underpins solution and electrochemistry numericals.

Spaced revision: Review this note at 1 day, 3 days, and 7 days after first study. Attempt the Quick check questions closed-book, then open the Practice tab for graded reinforcement. Maintain an error log — repeated mistake patterns reveal whether the issue is concept, formula recall, or careless reading.

Diagram and terminology drill: For Chemistry, redraw key figures from memory and define every labelled part in one sentence. Vocabulary precision prevents mark loss in descriptive answers — use NCERT terms exactly as printed in the textbook.

Revision tip: Link this topic to adjacent Class 12 chapters before attempting mixed practice.

Open the Practice tab for graded questions on Electrochemical Cells.