Coupled Reactions
Mediumchemistry
A non-spontaneous reaction can proceed if coupled with a more exergonic one because total ΔG:
Select the correct option:
Solution
Incorrect! Answer:
Becomes negative
- Coupling Mechanism: In many systems (especially biological ones), a non-spontaneous reaction (+ΔG1) is linked to a highly spontaneous one (−ΔG2).
- Additive Property: Gibbs free energy is an extensive state function. For back-to-back reactions, the total change is the sum of individual changes.
- Result: If ∣−ΔG2∣>∣+ΔG1∣, then the overall ΔGtotal becomes negative.
- Conclusion: The energy released by the downhill reaction 'drives' the uphill one. For example, ATP hydrolysis drives protein synthesis.
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About This Question
- Subject
- chemistry
- Chapter
- chemical thermodynamics
- Topic
- coupled reactions
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
Becomes negative
- Coupling Mechanism: In many systems (especially biological ones), a non-spontaneous reaction (+ΔG1) is linked to a highly spontaneous one (−ΔG2).
- Additive Property: Gibbs free energy is an extensive state function. For back-to-back reactions, the total change is the sum of individual changes.
- Result: If ∣−ΔG2∣>∣+ΔG1∣, then the overall ΔGtotal becomes negative.
- Conclusion: The energy released by the downhill reaction 'drives' the uphill one. For example, ATP hydrolysis drives protein synthesis.
This medium difficulty chemistry question is from the chapter chemical thermodynamics, covering the topic of coupled reactions. It appeared in the 2025 exam.
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