Q.6 Increase in the half-cell potential (E°)
- Decreases the oxidizing ability
- Increases the reducing ability
- Increases the oxidizing ability
- Increases the reaction spontaneity
Understanding Increase in Half-Cell Potential (E°)
An increase in the half-cell potential (E°) fundamentally alters redox behavior in electrochemical cells. This concept is crucial for students preparing for exams in biochemistry and molecular biology, where electrochemistry underpins techniques like voltammetry and enzyme kinetics.
Question Breakdown
The multiple-choice question asks: Increase in the half-cell potential (E°)
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Decreases the oxidizing ability
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Increases the reducing ability
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Increases the oxidizing ability
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Increases the reaction spontaneity
Standard half-cell potentials (E°) measure the tendency of a species to gain electrons (undergo reduction) relative to the standard hydrogen electrode (SHE, E° = 0 V). Higher (more positive) E° values indicate a stronger drive for reduction.
Option Analysis
Decreases the Oxidizing Ability
Incorrect. Oxidizing ability refers to how effectively the oxidized form accepts electrons from a reducing agent. An increase in E° strengthens this tendency, making the species a better oxidant—for example, Ag⁺ (E° = +0.80 V) oxidizes Cu more readily than Pb²⁺ (E° = -0.13 V). A decrease in E° would weaken oxidizing power.
Increases the Reducing Ability
Incorrect. Reducing ability is the capacity of the reduced form to lose electrons (undergo oxidation). This is stronger for half-cells with more negative E° values, like Zn²⁺/Zn (E° = -0.76 V), which readily donates electrons. An increase in E° (more positive) diminishes reducing strength, as the reduced form prefers to stay reduced.
Increases the Oxidizing Ability
Correct. A higher E° directly boosts the oxidizing strength of the oxidized species. In the electrochemical series, species like Au³⁺/Au (E° = +1.50 V) are superior oxidants compared to Cu²⁺/Cu (E° = +0.34 V). This is why increase in half-cell potential (E°) enhances the driving force for reduction.
Increases the Reaction Spontaneity
Partially correct but incomplete. Spontaneity in a full cell depends on E°_cell = E°_cathode (reduction) – E°_anode (oxidation), where positive E°_cell > 0 indicates ΔG < 0. While higher E° for the cathode increases E°_cell and spontaneity, the option is vague without cell context. The precise answer focuses on oxidizing ability.
Option Effect of ↑ E° Why Correct/Incorrect Decreases oxidizing ability Weaker oxidant Incorrect: Opposite effect Increases reducing ability Stronger reductant Incorrect: Reducing agents have low E° Increases oxidizing ability Stronger oxidant Correct: Higher E° favors reduction Increases reaction spontaneity More positive E°_cell Vague; depends on full cell Key Takeaways for Exam Prep
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Increase in half-cell potential (E°) prioritizes oxidizing ability in reduction half-reactions.
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Use E° tables to predict spontaneity: Pair high E° (cathode) with low E° (anode).
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Relate to Nernst equation for non-standard conditions: E = E° – (RT/nF) ln Q, where ↑[oxidized] boosts E.
This increase in half-cell potential (E°) principle clarifies redox hierarchies in biological systems, like electron transport chains. Master it for competitive exams!
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