ATP Hydrolysis and Bond Enthalpy

[Ashish]

Hey guys,

I just ran into some contradicting concepts and can't figure out which one is wrong. I Biochemical pathways like respiration and photosynthesis, we are told that energy is generated or given away when ATP breaks down into ADP, AMP and so forth (delta H < 0, exergonic) But when doing Bond enthalpy problems in general chem, the example states that delta H is positive when bond breaks (endergonic process).

Any explanation to this is greatly appreciated.

Thanks

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[Likkriue]

Atoms like being bonded together, because of entropy. Everything moves towards a higher entropy naturally. Because that's what the universe likes. The thing about ATP is that, it's not a very stable molecule, so while hydrolysis does take energy, the amount of energy released going from unstable to stable is better.

Molecules and atoms bond together to decrease their energy level; because they like being stable. As Chad said, the universe likes stable molecules like how girls like stable guys. BUT you can't just mash together any ol molecule. Not all bonds are stable, thus some atoms release energy when getting cleaved. Molecules don't bond together to get more unstable, they prefer to bond together to get more stable.

This is the best I can do, hope it helps.

 

[juandhy]

Great question! Chad explains this really well in one of his videos.

Breaking a bond IS endorgonic in enthalpy: by breaking a bond you take the molecules from a stable to a less stable (higher) energy level. This requires energy from the surroundings to accomplish.

With ATP to ADP however, a bond isn't merely breaking, it's a whole process. This mechanism makes a bond as well as breaks another. The OVERALL delta H turns out to be negative (exergonic).

We're taught ATP simply breaks bonds for simplicity sake, but there's more to the process than that.

 

[Ashish]

Great. Thanks guys. I did finally get to that Chad's video as well.