Using your knowledge of intermolecular forces, explain or answer the following:

a$)$ At $100C$ and $\frac{50}{b}ar,$ the compressibility factor $z$ for ethane gas is less than unity. However, at the same temperature and pressure the compressibility factor for helium gas is larger than unity.

b$)C{H}_2{F}_2$ has a dipole moment of $1\mathrm{.}93D$ and a boiling point of $-52CC{H}_{2}C{l}_2$ has a dipole moment of $1\mathrm{.}60D$ and a boiling point of $40C.$ Why is the boiling point of dichloromethane $92C$ higher than that of difluoromethane?

c$)$ An absorber operating at $0C$ and $600$ psia uses heptane to absorb ethane and propane from natural gas. It is found that heptane losses due to evaporation constitute a significant economic cost and it is therefore decided to lower the operating temperature to $-20oC.$ However, after this is done, it is found that heptane losses have increased rather than decreased.