# Deriving the equation for lines of constant enthalpy

 P: 1 How would one derive the equation for (dP/dV)H? That is the partial of P over the partial of V, holding H constant. I've tried many different things, triple product rule, maxwell relationships, and nothing seems to work. I appreciate any advice.
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 Quote by djkuehlos14 How would one derive the equation for (dP/dV)H? That is the partial of P over the partial of V, holding H constant. I've tried many different things, triple product rule, maxwell relationships, and nothing seems to work. I appreciate any advice.
You need to start with the equation of state, and write
$$dT=(\frac{\partial T}{\partial P})_VdP+(\frac{\partial T}{\partial V})_PdV$$

You need to combine this with the equation:

$$dH=C_PdT+(V-T(\frac{\partial V}{\partial T})_P)dP$$

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