Partial derivatives of enthelpy and Maxwell relations

In summary, the conversation is discussing the use of Maxwell relations and the definitions of ##\alpha##, ##\kappa##, and ##c## to continue a problem. The speaker also provides a way to rewrite certain partial derivatives using the given equations.
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Homework Statement
Write the following partial derivatives in terms of heat capacity (##c##), compressibility (##\kappa##) and coefficient of thermal expansion (##\alpha##).

##(\frac{\partial H}{\partial V})_U##
##(\frac{\partial H}{\partial V})_S##

With ##H##: enthalpy, ##U##: internal energy, ##V##: volume, ##S##: entropy and the subscript denotes a magnitud held constant in differentiation.
Relevant Equations
##dH=dU+Pdv+vdP##
##dU=TdS-PdV##
I've attached images showing my progress. I have used Maxwell relations and the definitions of ##\alpha##, ##\kappa## and ##c##, but I don't know how to continue. Can you help me?
 

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  • #2
Your picture is unreadable.
 
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You have that ##H = U + PV##. And you also have that ##dU = T dS - P dV##. So when ##U## is constant, you have: ##dH = d(PV) = PdV + V dP##. And you also have when ##U## is constant, ##TdS - PdV = 0##. So we conclude:

##\frac{\partial H}{\partial V}|_U = P + V \frac{\partial P}{\partial V}|_U##

Now, if you think of ##P## as a function of ##S## and ##V##, then

##\frac{\partial P}{\partial V}|_U = \frac{\partial P}{\partial V}|_S + \frac{\partial P}{\partial S}|_V \frac{\partial S}{\partial V}|_U##

At this point, you can use ##TdS - PdV = 0## (when ##dU = 0##) to rewrite ##\frac{\partial S}{\partial V}|_U##, and you can use one of the Maxwell relations to rewrite ##\frac{\partial P}{\partial S}|_V##.
 
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1. What is a partial derivative of enthalpy?

A partial derivative of enthalpy is a mathematical concept used in thermodynamics to measure the rate of change of enthalpy with respect to a specific variable. It represents the change in enthalpy of a system when only one of its variables is allowed to vary, while all other variables are held constant.

2. How is a partial derivative of enthalpy calculated?

A partial derivative of enthalpy can be calculated using the chain rule of calculus. This involves taking the derivative of the enthalpy function with respect to the variable of interest, while treating all other variables as constants.

3. What are Maxwell's relations in thermodynamics?

Maxwell's relations are a set of four equations that relate the partial derivatives of thermodynamic variables, such as enthalpy, temperature, and pressure. They are derived from the fundamental thermodynamic equation and are used to simplify calculations in thermodynamics.

4. How are Maxwell's relations used in thermodynamics?

Maxwell's relations are used to simplify calculations in thermodynamics by relating different thermodynamic variables to each other. They can also be used to determine the values of certain thermodynamic properties that are difficult to measure directly.

5. What is the significance of partial derivatives of enthalpy and Maxwell's relations in thermodynamics?

Partial derivatives of enthalpy and Maxwell's relations are fundamental concepts in thermodynamics that help us understand the behavior of thermodynamic systems. They are used to analyze and predict the changes in energy, temperature, and other variables in a system, and are essential in the study of heat and energy transfer processes.

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