One mole of oxygen at $25\backslash$deg C and $15$atm is compressed iso$-$energetically $($i$.$e$.$ at constant

energy$)$ to $35$atm. Calculate the change in entropy using both a simple ideal gas $($ c$=$

$52)$ and a simple van der Waals fluid. The other parameters for the van der Waals

fluid can be found from the critical properties of oxygen, as shown in Section B$.3$ of

Appendix B$.$ Compare the two answers. Why are they different? How does your answer

fit with the definition of entropy, S$($U$,$ V$,$N$)$ :$=$ KB log$\backslash$Omega $($U$,$ V$,$N$)?$