What is the relationship between entropy and pressure in thermodynamics?

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SUMMARY

The discussion focuses on deriving the relationship between entropy (S) and pressure (P) in thermodynamics, specifically calculating the partial derivative \((\frac{\partial H}{\partial P})_T\) in terms of pressure, volume (V), temperature (T), thermal expansion coefficient (\(\beta\)), isothermal compressibility (\(\kappa\)), and specific heat at constant pressure (\(c_p\)). The user employs various thermodynamic identities and differentials, including \(dS\) and \(dG\), to manipulate the equations. The final expression derived is \((\frac{\partial H}{\partial P})_T = -(\frac{\partial H}{\partial S})_P (\frac{\partial S}{\partial H})_P (\frac{\partial H}{\partial T})(\frac{\partial T}{\partial P})\), indicating a complex interdependence of these variables.

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  • Understanding of thermodynamic identities and equations
  • Familiarity with partial derivatives in thermodynamics
  • Knowledge of specific heat, thermal expansion, and compressibility
  • Proficiency in manipulating differential forms in thermodynamic contexts
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This discussion is beneficial for thermodynamics students, researchers in physical chemistry, and professionals working in fields involving heat transfer and material properties.

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Homework Statement
Derive ##(\frac{\partial H}{\partial P})_t## in term of ##P,V,T, \beta, \kappa, c_p##
Let H = H(T,P)
Relevant Equations
##ds = (\frac{\partial S}{\partial H})_p dH + (\frac{\partial S}{ \partial P})_H dP##

##dH = (\frac{\partial H}{\partial T})_p dT + (\frac{\partial H}{ \partial P})_T dP##
Hi,
Starting from dS in term of H and P, I'm trying to find ##(\frac{\partial H}{\partial P})_t## in term of ##P,V,T, \beta, \kappa, c_p##.
Here what I did so far.

##ds = (\frac{\partial S}{\partial H})_p dH + (\frac{\partial S}{ \partial P})_H dP##

##ds = (\frac{\partial S}{\partial H})_p [ (\frac{\partial H}{\partial T})_p dT + (\frac{\partial H}{ \partial P})_T dP] + (\frac{\partial S}{ \partial P})_H dP##

##\frac{\partial S}{\partial P} = (\frac{\partial S}{\partial H})_p (\frac{\partial H}{\partial T}) (\frac{\partial T}{\partial P}) + (\frac{\partial H}{\partial P})_T (\frac{\partial S}{\partial H})_P + (\frac{\partial S}{\partial P})_H##

##(\frac{\partial S^2}{\partial T \partial P}) = (\frac{\partial S}{\partial H})_p (\frac{\partial H}{\partial T}) (\frac{\partial T}{\partial P}) + (\frac{\partial H}{\partial P})_T (\frac{\partial S}{\partial H})_P + \frac{d}{dP}(\frac{\partial S}{\partial P})_H##

##(\frac{\partial H}{\partial P})_T = -(\frac{\partial H}{\partial S})_P (\frac{\partial S}{\partial H})_P (\frac{\partial H}{\partial T})(\frac{\partial T}{\partial P})##

From there, I'm stuck. I don't see how I can get ##P,V,T, \beta, \kappa, c_p##

Thank you
 
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Start with the exact differential dG=-SdT+VdP, which means that $$\left(\frac{\partial S}{\partial P}\right)_T=-\left(\frac{\partial V}{\partial T}\right)_P$$
 
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I have to start with ds in term of dh and dp.
I just saw in the original post, those P should be in index.

I finally found something using ##Tds = dh - vdp##
 
Last edited:

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