## Homework #8.71

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

Melissa Trieu 1K
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### Homework #8.71

For number 71, I do not understand why both reaction 2 and 3 are multiplied by 3. I understand that reaction 2 is multiplied by 3 to get 3 moles of NADH but why reaction 3? And why do we divide the total Gibbs free energy of reaction 2 and 3 by reaction 1's Gibb's free energy?

Chem_Mod
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### Re: Homework #8.71

This question is tricky because it touches upon the topic of the Electrochemistry chapter. Notice that reactions (2) and (3) involve electrons, and as you will learn soon, these are actually "half-reactions". Adding them together cancels out the electrons and gives a total reaction that represents the actual consumption of NADH. Adding up their deltaG's gives the total deltaG also.

So now we have only two reactions, call them (1) for the synthesis of ATP and (2+3) for the oxidation of NADH. The ratio of their deltaG's tells us how many ATP can be made per NADH.