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Topic: Somebody help me,about a plot  (Read 2568 times)

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Offline Ali-x

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Somebody help me,about a plot
« on: April 17, 2015, 07:30:05 AM »
Hello everybody,Lately i mixed up with a plot in thermodynamics
Differentiation of Gibbs energy over differentiation of temperature at constant pressure is -S
It shows that when T is increasing S is not increasing,it is constant(better to say it is linear)
So this interpretation doesn't sound good because when you heat something you increase its entropy.
Could any body help me?

Offline mjc123

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Re: Somebody help me,about a plot
« Reply #1 on: April 17, 2015, 08:24:51 AM »
To say that dG/dT = -S does not necessarily imply that S is constant.
However, if it is not, why is there no dS/dT term?
Write the expression for G, differentiate it, and see if you can eliminate everything except -S.

Offline Ali-x

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Re: Somebody help me,about a plot
« Reply #2 on: April 17, 2015, 09:29:00 AM »
Many thanks for your reply
You i got confused because the G derivative expression says -s but my knowledge about increasing temperature doesn't imply with pure theoretical derivation.
Is it kind of shortcoming of theory and empirical?

Offline Ali-x

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Re: Somebody help me,about a plot
« Reply #3 on: April 17, 2015, 10:00:42 AM »
To say that dG/dT = -S does not necessarily imply that S is constant.
However, if it is not, why is there no dS/dT term?
Write the expression for G, differentiate it, and see if you can eliminate everything except -S.
Many thanks for your reply
You i got confused because the G derivative expression says -s but my knowledge about increasing temperature doesn't imply with pure theoretical derivation.
Is it kind of shortcoming of theory and empirical?

Offline mjc123

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Re: Somebody help me,about a plot
« Reply #4 on: April 17, 2015, 10:49:44 AM »
No. G = H - TS
Differentiate that (assuming H and S are not constant with temperature).
What does (dH/dT)P equal? What does (dS/dT)P equal? So...

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