Coupled Reactions

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A non-spontaneous reaction can proceed if coupled with a more exergonic one because total ΔG:

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1. **Coupling Mechanism**: In many systems (especially biological ones), a non-spontaneous reaction ($+ \Delta G_1$) is linked to a highly spontaneous one ($-\Delta G_2$).
2. **Additive Property**: Gibbs free energy is an extensive state function. For back-to-back reactions, the total change is the sum of individual changes.
3. **Result**: If $|−\Delta G_2| > |+\Delta G_1|$, then the overall **$\Delta G_{	ext{total}}$ becomes negative**.
4. **Conclusion**: The energy released by the downhill reaction 'drives' the uphill one. For example, ATP hydrolysis drives protein synthesis.

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Coupled Reactions

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