Ways to calculate Gibbs free energy


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ashwathinair
Posts: 113
Joined: Sat Aug 17, 2019 12:17 am

Ways to calculate Gibbs free energy

Postby ashwathinair » Sun Mar 01, 2020 10:29 pm

For cell/redox problems, when do we use deltaG = deltaH - TdeltaS and deltaG = deltaG(products) - deltaG(reactants)?

ASetlur_1G
Posts: 101
Joined: Fri Aug 09, 2019 12:17 am

Re: Ways to calculate Gibbs free energy

Postby ASetlur_1G » Sun Mar 01, 2020 11:16 pm

I think it mostly just depends on what they give you. If you're given a table with delta G of different molecules, then you use the second one.

Hussain Chharawalla 1G
Posts: 100
Joined: Sat Jul 20, 2019 12:15 am

Re: Ways to calculate Gibbs free energy

Postby Hussain Chharawalla 1G » Sun Mar 01, 2020 11:23 pm

You use the second equation when given gibbs free energy standard formation measurements. You use the first equation when given enthalpy and entropy.

ashwathinair
Posts: 113
Joined: Sat Aug 17, 2019 12:17 am

Re: Ways to calculate Gibbs free energy

Postby ashwathinair » Mon Mar 02, 2020 10:31 am

ASetlur_1G wrote:I think it mostly just depends on what they give you. If you're given a table with delta G of different molecules, then you use the second one.


I understand this, but for one of the homework questions (5J 15), we were supposed to use different methods of finding deltaG at different temperatures (25 and 150 degrees Celsius). Why did we have to do that?

Timmy Nguyen Dis 1I
Posts: 107
Joined: Sat Aug 17, 2019 12:17 am

Re: Ways to calculate Gibbs free energy

Postby Timmy Nguyen Dis 1I » Mon Mar 02, 2020 10:57 am

It depends on what the problem is asking for.

Brandi 2C
Posts: 52
Joined: Thu Feb 28, 2019 12:15 am

Re: Ways to calculate Gibbs free energy

Postby Brandi 2C » Mon Mar 02, 2020 11:48 am

ashwathinair wrote:
ASetlur_1G wrote:I think it mostly just depends on what they give you. If you're given a table with delta G of different molecules, then you use the second one.


I understand this, but for one of the homework questions (5J 15), we were supposed to use different methods of finding deltaG at different temperatures (25 and 150 degrees Celsius). Why did we have to do that?



I also had confusion around this question in the homework. If we are supposed to use the first equation for the 25C and then the van't Hoff equation for 150C, then how do you find delta G for the first part because it says to find the appropriate values in the appendix but I can't find the NH4Cl delta G?


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