What is the relationship between entropy and pressure in thermodynamics?

In summary, the conversation discusses finding the partial derivative of H with respect to P in terms of P, V, T, β, κ, and c_p. The conversation includes several equations and the speaker mentions being stuck and unsure how to proceed. The expert suggests starting with the exact differential dG=-SdT+VdP and using the equation Tds = dh - vdp to find the desired partial derivative.
  • #1
happyparticle
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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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  • #2
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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Likes vanhees71
  • #3
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:

FAQ: What is the relationship between entropy and pressure in thermodynamics?

What is the Joule Thomson coefficient?

The Joule Thomson coefficient, also known as the Joule Thomson effect or the Joule Kelvin effect, is a thermodynamic property that describes the change in temperature of a gas when it undergoes a throttling process at constant enthalpy.

How is the Joule Thomson coefficient calculated?

The Joule Thomson coefficient is calculated by taking the partial derivative of the temperature with respect to pressure at constant enthalpy. This can be represented by the equation μ = (∂T/∂P)H, where μ is the Joule Thomson coefficient, T is the temperature, P is the pressure, and H is the enthalpy.

What is the significance of the Joule Thomson coefficient?

The Joule Thomson coefficient is important in understanding the behavior of gases under different conditions. It helps to predict the temperature change of a gas when it is expanded or compressed, and is used in various industrial processes such as refrigeration and natural gas processing.

What factors affect the Joule Thomson coefficient?

The Joule Thomson coefficient is affected by the type of gas, its temperature and pressure, and the properties of the gas molecules such as size and intermolecular forces. It also varies with the conditions of the throttling process, such as the rate of expansion or compression.

How does the Joule Thomson coefficient differ from the coefficient of thermal expansion?

The Joule Thomson coefficient is a measure of the change in temperature due to a change in pressure at constant enthalpy, while the coefficient of thermal expansion is a measure of the change in volume due to a change in temperature at constant pressure. In other words, the Joule Thomson coefficient describes the relationship between pressure and temperature, while the coefficient of thermal expansion describes the relationship between volume and temperature.

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