Question #9 in Quiz 1 Winter 2015

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Hailey Donaldson 1E
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Question #9 in Quiz 1 Winter 2015

Postby Hailey Donaldson 1E » Mon Jan 25, 2016 6:50 pm

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
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Re: Question #9 in Quiz 1 Winter 2015

Postby Ronald Yang 2F » Mon Jan 25, 2016 7:10 pm

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

Postby Chem_Mod » Mon Jan 25, 2016 7:33 pm

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



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

=0

ShangShi1K
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Re: Question #9 in Quiz 1 Winter 2015

Postby ShangShi1K » Mon Jan 25, 2016 10:33 pm

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
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Re: Question #9 in Quiz 1 Winter 2015

Postby Rita Tran 2B » Mon Jan 25, 2016 11:17 pm

Can someone explain why and are 0? How do you determine this value?


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