Calculating deltaG at different temps






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sofiakavanaugh
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Joined: Thu Jul 13, 2017 3:00 am
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Calculating deltaG at different temps

Postby sofiakavanaugh » Tue Feb 13, 2018 4:28 pm

Hi,

For problems where we are doing deltaG calculations for phase changes, I understand we need to calculate deltaH and deltaS values from appendix 2A first and then calculate delta G. My question is, when we use to calculate deltaH individually for phase changes sometimes we would have to add a q=mcat if it wasn’t already at the boiling/melting temp to the deltaH fusion/vap to get the accurate deltaH. My question is, do we need to do that and incorporate that factor when calculating deltaG of phase changes from our deltaH And deltaS values? An example of this would be 9.91.

Thanks!

Chem_Mod
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Re: Calculating deltaG at different temps

Postby Chem_Mod » Tue Feb 13, 2018 6:17 pm

Hi, Sofia,
deltaG = deltaH-TdeltaS. T in this equation accounts for any temperature at which a phase change takes place. Both delta H and delta S that are used in this equation are found for the temperature of the phase change (e.g. 0 for melting of ice). You don't need to do anything else to delta H and delta S.


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