AP Chemistry / Unit 9: Thermodynamics and Electrochemistry
9.7 Coupled Reactions
Notes
An unfavorable reaction ($\Delta G>0$) can be driven by pairing it with a very favorable one so the total $\Delta G<0$.
- Biology: ATP hydrolysis drives many reactions.
- External energy (light, electricity) can also drive reactions.
Practice
Reaction 1: $\Delta G=+20$ kJ. Reaction 2: $\Delta G=-30$ kJ. Coupled $\Delta G$:
$20-30$.
Coupling works when the combined $\Delta G$ is:
The sum must be favorable.
Cells drive unfavorable reactions using:
Energy coupling.
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