Can internal energy be calculated from equation of state?

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SUMMARY

The discussion centers on calculating internal energy using the equation of state, specifically through the relationship \(dU=TdS-PdV\). The user explores expressing entropy \(S\) as a function of pressure \(P\), volume \(V\), or temperature \(T\) using Maxwell's relations. It is established that while terms can be derived from the equation of state, the term \(\left(\frac{\partial V}{\partial T}\right)_S\) requires additional information, specifically the heat capacity, to complete the calculation. The consensus is that both the equation of state and heat capacity are essential for accurate internal energy calculations.

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  • Understanding of thermodynamic principles, specifically internal energy and entropy.
  • Familiarity with Maxwell's relations in thermodynamics.
  • Knowledge of equations of state for various substances.
  • Basic concepts of heat capacity and its role in thermodynamic calculations.
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  • Study the derivation and application of Maxwell's relations in thermodynamics.
  • Research specific equations of state for different materials, such as the Van der Waals equation.
  • Learn about heat capacity and its significance in thermodynamic processes.
  • Explore advanced thermodynamic calculations involving internal energy and entropy changes.
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Students and professionals in thermodynamics, physicists, and engineers involved in energy calculations and material properties analysis.

arpon
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We know,
$$dU=TdS-PdV$$
##\int PdV## can be calculated if the equation of state is given.
I tried to express ##S## as a function of ##P ,V## or ##T## (any two of those).
$$dS=\left(\frac{\partial S}{\partial V}\right)_T dV+\left(\frac{\partial S}{\partial T}\right)_V dT$$
$$=\left(\frac{\partial P}{\partial T}\right)_V dV+\left(\frac{\partial S}{\partial P}\right)_V \left(\frac{\partial P}{\partial T}\right)_V dT~~~ [Using ~~Maxwell's~~ relation]$$
$$=\left(\frac{\partial P}{\partial T}\right)_V dV-\left(\frac{\partial V}{\partial T}\right)_S \left(\frac{\partial P}{\partial T}\right)_V dT~~~[Using ~~Maxwell's~ ~relation]$$
All the terms except ##\left(\frac{\partial V}{\partial T}\right)_S## can be calculated using the equation of state.
Any suggestion will be appreciated.
 
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You can't do it solely in terms of the equation of state. You need to use the heat capacity as well.
 
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Chestermiller said:
You can't do it solely in terms of the equation of state. You need to use the heat capacity as well.
Thanks. That's exactly what I wanted to know.
 

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