## Knowing when a value is equal to zero

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

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

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

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Rachael_1H
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Joined: Fri Sep 25, 2015 3:00 am

### Knowing when a value is equal to zero

A sample of one mole of gas initially at one ATM and 298 K is heated at constant pressure to 350 K then the gas is compressed isothermally to its initial volume and finally it is cooled to 298 K at constant volume. Which of the following values is zero?

Delta S surroundings and Delta G
Delta S system and Delta S surroundings
q and w
W
Delta G and Delta S system

The answer key says The correct answer is "delta G and delta S system."

How did the answer key get this answer? What is the most efficient way to go about this problem?

Chem_Mod
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### Re: Knowing when a value is equal to zero

The initial state of your system is 1 atm, 298K and some volume v1. After all the transformations, the system ends at 298K and the initial volume v1. So after all the heatings and compressions, the initial and final states of the system are identical. Since no change has occured, the delta S and delta G of the system will be zero.

Yoon Lee 2A
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

### Re: Knowing when a value is equal to zero

Why isn't delta S surr also zero since it is also a state function?

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