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Coupled Reactions

Coupled reactions involve pairing a spontaneous reaction (ΔG < 0) with a non-spontaneous reaction (ΔG > 0) to drive the latter forward. This concept is essential in biological and chemical systems where energy transfer is required.

How Coupled Reactions Work​

  • The overall ΔG for coupled reactions is additive:
    ΔG_total = ΔG_spontaneous + ΔG_non-spontaneous
  • A non-spontaneous reaction can proceed if it is coupled with a reaction that releases enough free energy to make ΔG_total negative.

Common Examples​

  • ATP Hydrolysis:
    • ATP → ADP + Pi (ΔG < 0)
    • Drives many non-spontaneous cellular processes like muscle contraction or active transport.
  • Redox Reactions in Metabolism:
    • Electron transfer from a high-energy donor to a lower-energy acceptor provides energy to drive other biochemical reactions.

Key Points​

  • Coupled reactions are crucial for energy management in chemical and biological systems.
  • They allow reactions that would otherwise not occur spontaneously to proceed efficiently.
  • Understanding ΔG and energy coupling is fundamental for thermodynamics and biochemistry applications.

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