Winter Midterm 2016: Q5A

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Winter Midterm 2016: Q5A

Postby megan_thi_2j » Wed Feb 15, 2017 3:25 pm

I was wondering why for part A of this question, the reaction with the higher standard Gibbs free energy is reversed?

Joseph Nguyen 3L
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Re: Winter Midterm 2016: Q5A

Postby Joseph Nguyen 3L » Wed Feb 15, 2017 3:34 pm

The fact that it is reversed has nothing to do with the fact that it has a higher Gibbs free energy. For hydrolysis, they give you a certain reaction. Because you want H20 on the reactant side and HPO4^2- on the product side, you flip reaction 2 which makes it negative and now both sides can cancel out when added. You know that you can add the two free energies because delta G is a state function.

Joyce Wu 3E
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Re: Winter Midterm 2016: Q5A

Postby Joyce Wu 3E » Wed Feb 15, 2017 3:39 pm

Whether or not the reaction is reversed is based off of the overall equation that is given in the problem. It was ATP+H2O --> ADP + (HPO4)2-
Seeing the 2 reactions given, we see that we needed the fructose molecules to cancel out while having the products and reactants from the given equation stay in the same place. Therefore, we flip reaction 2 to cancel out the fructose. The higher positive of the deltaG doesn't matter in this problem. You might be confusing this concept with standard cell potential (E)

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