An exergonic reaction is one for which Delta G 0. One of the chemical reactions

Question

An exergonic reaction is one for which Delta G 0. One of the chemical reactions that cells commonly use to release energy is the hydrolysis of ATP (adenosine triphosphate) to ADP (adenosine diphosphate). At pH = 7.0, this reaction is exergonic Delta G_rxn = -31 kJ/mol: ATP^4- (aq) + H_2 O(l) rightarrow ADP^3_ (aq) + HPO_4^2- (aq) + H_3 O^+ (aq) a. The negative value of Delta G is partially thought to arise from the entropy change associated with this reaction. Why should this be the case? b. Electrostatic repulsion between the phosphate groups of ATP may also contribute to the free energy of this reaction. How would electrostatic repulsion affect Delta G? c. Stabilization via resonance in ATP^4- and HPO_4^2- also impacts the free energy change of the ATP^4- hydrolysis reaction. Does resonance impact Delta G through, Delta, Delta through both terms?

Explanation / Answer

a) The hydrolysis of phosphoanhydric bonds is spontaneous process and is highly exergonic. The reaction when coupled with a thermodynamically unfavourable reaction gives an overall negative delta G for the reaction.

b) The electrostatic repulsion of phosphate group makes the reaction energetically more favourable and spontaneous with the release of free energy. If reaction is spontaneous then the delta G is negative.

c) Yes the resonance impacts delta Grxn and delta Srxn (which is entropy change. Large entropy change occurs). Large enthalpy change(delta Hrxn) does not occur.

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