I'm having a problem where I have to derive the equation of state of an ideal gas from the formula for molar heat capacity $C=C_V+ \beta V$. Is this even ideal gas? Can someone help me, or at least give me a clue on how to solve this problem?

  • $\begingroup$ What is the exact word-for-word statement of the problem? $\endgroup$ – Chet Miller Jun 14 '19 at 11:43
  • $\begingroup$ I forgot. I have to do it for an exam, and I went home remembering it like this. Just want to know the answer since the teacher is unlikely to release solutions until someone solves it (he reused exam question lol) $\endgroup$ – Kim Dong Jun 15 '19 at 8:59
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    $\begingroup$ I'm assuming an ideal gas since the goal is find the equation from the heat capacities. $dQ=dU+dW, dU=C_{v}dT \rightarrow dQ=C_{V}dT+dW$. $dQ=dH-VdP, dH=C_{p}dT \rightarrow dQ=C_{P}dT-VdP$. Hence, $C_{V}dT+dW=C_{P}dT-VdP$ implies $C_{V}dT+PdV=C_{P}dT-VdP$ where $dW=PdV$. Hence $RdT=d(PV)$ where the molar heat capacities $C_{P}-C_{V}=nR$. Or $PV=nRT$ $\endgroup$ – Cinaed Simson Jun 15 '19 at 19:36

You have to use the Maxwell thermodynamical relations to derive a potential. Most likely you need to start from $$\frac{\partial U}{\partial T} = C_{V}\\C=\frac{\partial Q}{\partial T}$$

Take a look at the thermodynamic square, maybe you will first need to derive a potential ($U$?). Once you have a potential it is trivial to get the equation of state.


https://en.wikipedia.org/wiki/Table_of_thermodynamic_equations https://en.wikipedia.org/wiki/Thermodynamic_square


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