Free energy vs. Free energy change Khan Q

[DanniD]

How does the free energy (G) of a system containing one mole of ADP compare to the free energy of a system containing one mole of AMP under standard physiological conditions?

hi guys I dont get why ADP has more positive free energy compared to AMP. according to Khan "The free energy of a system can never be negative. Remember, free energy (G) is not the same as free energy change (∆G)."

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[Neuroplasticity]

ADP is adenosine diphosphate and AMP is adenosine monophosphate

ADP has 1 more phosphate group, giving it a higher enthalpy because of the energy stored in those bonds. G=H-TS, so higher enthaply gives higher free energy (G).

 

[DanniD]

ADP is adenosine diphosphate and AMP is adenosine monophosphate

ADP has 1 more phosphate group, giving it a higher enthalpy because of the energy stored in those bonds. G=H-TS, so higher enthaply gives higher free energy (G).

hey thanks for the explanation, my problem is why they say that "free energy (G) can never be negative"

I guess because free energy is found from this equation GA = GA° + RT ln PA whereas, free energy CHANGE is sum of the free energies of the products, minus that of the reactants: ΔG = GC + GD – GA – GB so thats why free energy CHANGE could be negative whereas free energy can never be negative?

 

[Neuroplasticity]

hey thanks for the explanation, my problem is why they say that "free energy (G) can never be negative"

I guess because free energy is found from this equation GA = GA° + RT ln PA whereas, free energy CHANGE is sum of the free energies of the products, minus that of the reactants: ΔG = GC + GD – GA – GB so thats why free energy CHANGE could be negative whereas free energy can never be negative?

Sorry, I just saw you said "I dont get why ADP has more positive free energy compared to AMP" and responded to that. Yes, I think you have understood your confusion. It is similar to kinetic energy. An object can have a negative change in kinetic energy, but it can't have negative kinetic energy (unless some physicist wants to comment on objects with negative mass or something).

 

[DanniD]

Sorry, I just saw you said "I dont get why ADP has more positive free energy compared to AMP" and responded to that. Yes, I think you have understood your confusion. It is similar to kinetic energy. An object can have a negative change in kinetic energy, but it can't have negative kinetic energy (unless some physicist wants to comment on objects with negative mass or something).

great analogy! thanks for the clarification!