Q.33 Given that ΔG = ΔH − TΔS, with reference to it, identify the wrong statement:
- In exergonic reaction, ΔG is negative.
- When ΔG is zero, the system is at equilibrium.
- ΔG must be positive for the reaction to be spontaneous.
- In exergonic reaction ΔG is always equals to 1.
ΔG must be positive for the reaction to be spontaneous is the wrong statement. For spontaneity under constant temperature and pressure, ΔG must be negative according to the Gibbs free energy equation ΔG = ΔH − TΔS.
Question Breakdown
This thermodynamics question evaluates understanding of Gibbs free energy (ΔG) signs and their implications for reaction spontaneity and equilibrium, key for biochemistry and physical chemistry in exams like GATE Life Sciences.
Statement Analysis
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In exergonic reaction, ΔG is negative: Correct. Exergonic reactions release free energy (ΔG < 0), driving them forward spontaneously.
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When ΔG is zero, the system is at equilibrium: Correct. ΔG = 0 means forward and reverse rates balance, with no net change.
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ΔG must be positive for the reaction to be spontaneous: Wrong. Spontaneous reactions require ΔG < 0; positive ΔG indicates non-spontaneous (endergonic).
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In exergonic reaction ΔG is always equals to 1: Wrong, but not the primary error here. ΔG is negative (not fixed at 1); magnitude varies by conditions.
Introduction to Gibbs Free Energy
The wrong statement ΔG = ΔH − TΔS exergonic reaction is “ΔG must be positive for the reaction to be spontaneous,” as ΔG < 0 defines spontaneity in biological and chemical systems.
This equation predicts if processes like ATP hydrolysis (exergonic, ΔG ≈ -30.5 kJ/mol) occur naturally.
Correct vs. Incorrect Statements
Statement Correct? Explanation Exergonic: ΔG negative Yes Drives forward (e.g., respiration) ΔG = 0: Equilibrium Yes No net reaction ΔG positive: Spontaneous No Actually non-spontaneous Exergonic ΔG = 1 No ΔG negative, not fixed value Applications in Life Sciences
In molecular biology, negative ΔG couples endergonic reactions (like biosynthesis) to exergonic ones via ATP. Equilibrium (ΔG=0) governs enzyme kinetics.
For exams, remember: spontaneous ≠ fast; ΔG predicts feasibility, not rate.
This builds on your biochemistry interests, linking to metabolic pathways and enzyme functions.
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