## Midterm 2007 Q3B- Explanation of (delta)S total

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

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

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

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Amy Luong 1L
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### Midterm 2007 Q3B- Explanation of (delta)S total

Would someone mind explaining why "delta S knot" is not a criterion for assessing the spontaneity of a reaction but the "delta S total rxn" shows that a reaction is spontaneous when it is greater than 0?

Satvir Saggi 1I
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### Re: Midterm 2007 Q3B

According to the second law of thermodynamics, "A spontaneous change is accompanied by an increase in the total entropy of the system and its surroundings." Therefore, we can only determine if a reaction is spontaneous based off the total change in entropy.

Chem_Mod
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### Re: Midterm 2007 Q3B- Explanation of (delta)S total

Satvir is correct. To be spontaneous, TOTAL entropy must be positive. If we don't want to care about the surroundings, then we must use deltaG. If deltaG at constant T and P of the system is negative, then it is also spontaneous.

Showing the equivalence of spontaneity conditions:
$\Delta S_{tot} > 0$
$\Delta S + \Delta S_{surr} > 0$
$\Delta S - \Delta H/T > 0$
$T\Delta S - \Delta H > 0$
$\Delta H - T\Delta S < 0$
$\Delta G < 0$

Justin Le 2I
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### Re: Midterm 2007 Q3B- Explanation of (delta)S total

since deltaG = deltaH - TdeltaS, we can't determine if a reaction is spontaneous if we are simply given deltaS. We need more information to see if deltaG is less than 0

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