Advanced Topic 373 of 1102 Thermodynamics & Energetics
Coupled Reactions
A spontaneous reaction can drive a nonspontaneous one, as ATP hydrolysis powers biosynthesis.
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In-depth explanation of Coupled Reactions
Coupled reactions are a strategy by which a nonspontaneous process is driven forward by linking it to a strongly spontaneous one through a shared intermediate or species. For the coupled pair to proceed, the total Gibbs energy change of the combined reactions must be negative, even though one component alone has a positive delta G. Living cells use this principle extensively, most notably with adenosine triphosphate, whose hydrolysis releases about 30.5 kJ per mole under standard conditions and drives biosynthetic reactions. The energy from ATP is transferred through phosphorylated intermediates, which keeps the coupling efficient. Coupling is thus the thermodynamic basis of metabolism.
Going deeper: Coupled Reactions
Key ideas: Add the delta G values of the two reactions. If the sum is negative, the pair is spontaneous together. The coupling needs a common intermediate or an enzyme to transfer energy, and the efficiency is never perfect.
Common mistakes and connections: Do not assume that simply mixing two reactions couples them, because a shared species or mechanism is required. In cells, ATP hydrolysis at about minus 30.5 kJ per mole under standard conditions, and more negative under cellular conditions, powers growth, movement and transport.
Visualization of Coupled Reactions
ATP hydrolysis (-30.5 kJ/mol) drives glucose phosphorylation (+13.8) so the combined delta G of -16.7 kJ/mol is spontaneous. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Phosphorylating glucose to glucose-6-phosphate has a positive delta G on its own, but coupling it to ATP hydrolysis makes the overall change negative.
Frequently asked questions about Coupled Reactions
What is Coupled Reactions?
A spontaneous reaction can drive a nonspontaneous one, as ATP hydrolysis powers biosynthesis.
Is Coupled Reactions a beginner, intermediate or advanced topic?
Coupled Reactions is a advanced topic in Thermodynamics & Energetics. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Coupled Reactions?
Study these earlier topics in Thermodynamics & Energetics first: Reaction Quotient and Free Energy, Free Energy and Work, Helmholtz Free Energy.
What comes after Coupled Reactions?
The next topics in Thermodynamics & Energetics are Reversible Process and Irreversible Process.
Can I practise Coupled Reactions with quizzes?
Yes. The interactive lesson includes a self-check question on Coupled Reactions, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Where Coupled Reactions fits in Thermodynamics & Energetics
Coupled Reactions is topic 45 of 91 in Thermodynamics & Energetics.