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I learned about the resonance stability of ADP and the fact that ATP is less stable due to intramolecular instability. I was surprised to see that the energy net of conversion of ADP to AMP is the same as ATP to ADP. Shouldn't the energy net of a reaction ADP to AMP+P be lower because it's not so readily hydrolysed?

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I learned about the resonance stability of ADP and the fact, that ATP is less stable due to intramolecular instability.

What you are probably refering to is an explanation why ADP and phosphate are more stable than ATP (and water). The explanation goes something like this:

[Tiffany Lui, University of California, Davis on Libretexts] Resonance stabilization of ADP and of Pi is greater than that of ATP. The oxygen molecules of the ADP are sharing electrons. Those electrons are constantly being passed back and forth between the oxygens, creating an effect called resonance. This stables the ADP. Resonance does not occur in ATP; therefore, it is a more unstable molecule.

Source: Libretexts

This argument has gone awry. First, you can't compare the stability of two species unless they contain the same set of atoms and have the same charge (see e.g. https://chemistry.stackexchange.com/a/146497). Second, the resonance stabilization on the terminal phosphate is similar for ADP and ATP. The better argument is that there is more resonance in ("inorganic") phosphate than in a phosphate ester or phosphoanhydride.

The experimental data shows that the energetics of ATP hydrolysis yielding ADP are very similar to ADP hydrolysis yielding AMP. In fact, there is an enzyme that turns ATP and AMP into two ADP, and the equilibrium constant for that reaction is close to 1:

$$\ce{ATP + AMP <=> 2ADP}$$

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ATP has two high energy bonds which are phosphoanhydride bonds. Both bonds release the same amount of energy. Therefore, when ATP converts to ADP, breaks one phosphoanhydride bond, and releases -30.5 kJ/mol. When the 2nd bond is broken in ADP releases -30.5 kJ/mol because it is the same phosphoanhydride bond. However, AMP has only a phosphate ester bond which releases -61 kJ/mol.

The "less stability" of ATP doesn't affect energy yield.

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    $\begingroup$ You are quoting Gibbs energy changes for the reaction with water at the biochemically defined standard state (neutral pH, some magnesium ions), $$\Delta_R G^{\circ \prime}$$ $\endgroup$
    – Karsten
    Feb 26, 2022 at 15:47
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    $\begingroup$ The term "high energy bond" is confusing to students as soon as they learn a bit of chemistry. It might be less confusing to say that ATP has a high phosphate group transfer potential, or simply that hydrolysis is an exergonic reaction. It is confusing because no bond "releases energy"; if it did, it would not form. Instead, the bonds formed after hydrolysis are stronger (electrons at lower energy) than those in place before hydrolysis. $\endgroup$
    – Karsten
    Feb 26, 2022 at 15:52
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    $\begingroup$ The Gibbs energy for a phosphate ester hydrolysis (e.g. AMP to adenosine) is on the order of -15 kJ/mol, not the -61 kJ/mol claimed. That value might be for ATP hydrolized to AMP and two phosphates. $\endgroup$
    – Karsten
    Feb 26, 2022 at 16:07

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