11. Hassium (Hs, Z=108), discovered in 1984, is believed to be one of the most dense elements known.
This is difficult to measure since it is highly radioactive. With an approximate MW=277 g/mol), and
assuming it crystallizes in a face centered cubic structure, calculate its density. The edge length (a) of
this cell is 0.4035 nm. 1 cm = 1 \times 10^{7} nm. (2 pts)
Extra Credit Problem
Both hydrazine and ammonia burn in oxygen to produce water and N$_2$ (g), with the balanced equations
given below.
\begin{itemize}
\item What is the enthalpy per kilogram for each? (1 pt)
\item On a mass basis (per kg) would hydrazine or ammonia be a better fuel? The molar mass of
hydrazine is 32.0 g/mol, molar mass of ammonia is 17.0 g/mol. (1 pt)
\end{itemize}
N$_2$H$_4$ (l) + O$_2$ (g) $\longrightarrow$ 2 H$_2$O (l) + N$_2$ (g) $\Delta$H = -622.02 kJ
4 NH$_3$ (g) + 3O$_2$ (g) $\longrightarrow$ 6 H$_2$O (l) + 2 N$_2$ (g) $\Delta$H = -1529.6 kJ
