## Question #9 in Quiz 1 Winter 2015

Hailey Donaldson 1E
Posts: 44
Joined: Fri Sep 25, 2015 3:00 am

### Question #9 in Quiz 1 Winter 2015

Question #9, on page 18 in the workbook reads, "A sample of 1 mole of gas initially at 1 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 298K at constant volume. Which of the following values is zero?"

I understand that the change in entropy (delta S) is 0, but the solution page states that both change in entropy and Gibbs' Free Energy are 0. Why is delta G also zero?

Ronald Yang 2F
Posts: 86
Joined: Fri Sep 25, 2015 3:00 am

### Re: Question #9 in Quiz 1 Winter 2015

delta G = delta H - T times delta S. Since the gas is "heated to 350 K" and "cooled back to 298 K," delta H is zero. Since delta H and delta S are both zero, delta G must also be zero.

Chem_Mod
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### Re: Question #9 in Quiz 1 Winter 2015

The question has a typo,

deltaGsys and deltaSsys both are equal to zero then both apply to the process of the system

Then you can think of it as

$\Delta H=\Delta U + P\Delta V$

The total change in volume and internal energy is zero so that term is zero

You also know that total change in entropy of the system is equal to zero

So the equation

$\Delta G=\Delta H-T\Delta S$=0

ShangShi1K
Posts: 17
Joined: Fri Sep 25, 2015 3:00 am

### Re: Question #9 in Quiz 1 Winter 2015

BTW, how to know (delta)Ssurr in this case?
CR gives the equation (delta)Ssurr=-(delta)Hsys/T, but if (delta)Hsys=0 shouldnt (delta)Ssurr=0 as well?

Rita Tran 2B
Posts: 25
Joined: Fri Sep 25, 2015 3:00 am

### Re: Question #9 in Quiz 1 Winter 2015

Can someone explain why $\Delta S_{sys}$ and $\Delta S_{surr}$ are 0? How do you determine this value?

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