Derive an expression for $(\frac{\text{d}\text{e}\text{l}\text{p}}{\text{d}\text{e}\text{l}\text{T}}{)}_{\frac{?}{\text{b}\text{a}\text{r}}(V)}$ for a van der Waals fluid. Check your expression using Python, and use Python to calculate the value of this derivative for the gas in problem $3$ above.

$(\frac{\text{d}\text{e}\text{l}\text{p}}{\text{d}\text{e}\text{l}\text{T}}{)}_{\frac{?}{\text{b}\text{a}\text{r}}(V)}$