Q.23 Oxidation reduction reactions with positive standard redox potential (ΔE°′) have
- (A) Positive ΔG°′
- (B) Negative ΔG°′
- (C) Positive ΔE°′
- (D) Negative ΔE°′
Oxidation-Reduction Reactions: Positive ΔE°′ Means Negative ΔG°′ Explained
Oxidation-reduction reactions with positive standard redox potential (ΔE°′) indicate spontaneous processes key to bioenergetics and biochemistry exams. The correct answer is (B) Negative ΔG°′, as it aligns with thermodynamic favorability.
Core Relationship
The standard redox potential ΔE°′ measures the tendency of a reaction to gain electrons, calculated as E°′(cathode) – E°′(anode). A positive ΔE°′ links directly to Gibbs free energy via ΔG°′ = -nFΔE°′, where n is electrons transferred and F is Faraday’s constant.
Since n and F are positive, positive ΔE°′ yields negative ΔG°′, signaling spontaneity without energy input.
Correct Answer: (B) Negative ΔG°′
Positive ΔE°′ drives forward reactions like cellular respiration, where electron flow releases energy. This negative ΔG°′ confirms exergonic processes essential in ATP synthesis and metabolism.
Option Analysis
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(A) Positive ΔG°′: Incorrect; positive ΔG°′ means endergonic, non-spontaneous reactions requiring energy, linked to negative ΔE°′.
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(B) Negative ΔG°′: Correct; as per ΔG°′ = -nFΔE°′, positive ΔE°′ ensures negative ΔG°′ for spontaneous redox like NADH oxidation.
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(C) Positive ΔE°′: Incorrect; this restates the premise without addressing consequences like ΔG°′.
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(D) Negative ΔE°′: Incorrect; negative ΔE°′ implies positive ΔG°′, non-spontaneous, as in electrolysis.
Option ΔE°′ Sign ΔG°′ Sign Spontaneity Example (A) Positive Positive No Reverse ETC step (B) Positive Negative Yes Glucose oxidation (C) Positive N/A Restates Premise only (D) Negative Positive No Water splitting Exam Relevance
In biotech and molecular biology exams, this tests bioenergetics understanding for topics like electron transport chains. Positive ΔE°′ values (e.g., O₂/H₂O at +0.82 V) ensure negative ΔG°′ for life’s energy harvest.
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