Intermediate Thermodynamics Questions & Answers  


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This is a good question. But before I answer, please edit your post and write the mathematics properly (with correct subscripts and same notation as in class).






It's getting there, but not close enough yet. Think about it more ;)




No, we did not assume that $P$ is constant when deriving the calorically perfect gas relationship $h=C_P T$. Rather we assumed that $C_P$ is a constant. What may be confusing you here is that $C_P$ is the socalled specific heat at constant pressure, which corresponds to: $$ C_P =\left(\frac{\partial h}{\partial T}\right)_P $$ The latter is true in the general case when the enthalpy depends on both pressure and temperature. But $h$ doesn't depend on pressure for a thermally perfect gas. Thus, for a thermally perfect gas $C_P$ becomes: $$ C_P =\frac{d h}{d T} $$ Thus, assuming constant $C_P$, we can then use $h=C_P T$ and this does not entail that $P$ should be constant. I'll give you one point for this question. I would have given more if you would have asked it with no typesetting mistake the first time around.



$\pi$ 