Gibbs free energy describes the maximum of useful work that can be done by a chemical reaction. My question is(Sorry I am not into chemistry and biochemistry) : during a chemical reaction that creates ATP, we say that ATP stores energy between its chemical bonds . For exemple this is the equation of creating ATP: ADP + Pi + energy ----> ATP and of course this reaction has DG. What is the relation of DG with the stored energy? Is it the same?


1 Answer 1


No, it can't be the same. If it were exactly the same, then it would mean that ATP was storing every last iota of available free energy. Another way of saying that is that ATP synthesis would be 100% energy efficient. That is, the free energy change $\Delta G$ in the reaction $\ce{ADP + Pi + energy -> ATP}$ would be zero.

But perfectly reversible reactions that have 100% efficiency never happen in the real world. Even theoretically, they can only happen at infintessimally slow rates.

Actual ATP synthesis isn't 100% efficient. It's efficiency depends on the details of the particular organism and its biochemistry, etc. Many organisms show efficiencies of 30 - 45% in the synthesis of ATP.

  • $\begingroup$ The useful work (DG) here is what then? $\endgroup$
    – Tonylb1
    Commented Oct 6, 2015 at 22:50
  • 1
    $\begingroup$ I saw the link. so the other DG is converted into heat right? but the term TDS in gibbs is also a part of the heat that cannot activate or do work on another reaction right? $\endgroup$
    – Tonylb1
    Commented Oct 7, 2015 at 3:32

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