3.25 Fundamental equations and exact differentials

We now relate Eq. (3.60) to the partial derivatives.

 \begin{equation*} \begin{split} dU = &\;\; T dS - p dV = \left(\frac{\partial U}{\partial S} \right)_V dS + \left(\frac{\partial U}{\partial V} \right)_S dV \quad \Rightarrow \quad \left(\frac{\partial U}{\partial S} \right)_V = T \qquad \left(\frac{\partial U}{\partial V} \right)_S = - p\\ dF = &\;\; - S dT - p dV = \left(\frac{\partial F}{\partial T} \right)_V dT + \left(\frac{\partial F}{\partial V} \right)_T dV \quad \Rightarrow \quad \left(\frac{\partial F}{\partial T} \right)_V = -S \qquad \left(\frac{\partial F}{\partial V} \right)_T = - p\\ dH = &\;\; T dS + V dp = \left(\frac{\partial H}{\partial S} \right)_p dS + \left(\frac{\partial H}{\partial p} \right)_S dp \quad \Rightarrow \quad \left(\frac{\partial H}{\partial S} \right)_p = T \qquad \left(\frac{\partial H}{\partial p} \right)_S = V\\ dG = &\;\; - S dT + V dp = \left(\frac{\partial G}{\partial T} \right)_p dT + \left(\frac{\partial G}{\partial p} \right)_T dp \quad \Rightarrow \quad \left(\frac{\partial G}{\partial T} \right)_p = - S \qquad \left(\frac{\partial G}{\partial p} \right)_T = V\\ \end{split} \label{eq:Guggenheim_exact_differentials} \end{equation*}(3.61)
These results clarify which exact differential with which restrictions have to be used/combined to get proper results related to the thermodynamic potentials.


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© J. Carstensen (TD Kin I)